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The Carbonate Buffer


  1. [M][some F] Buffering n' pH in marine tanks
    by (K. Rogers) (Thu, 11 Jun 1992)
  2. CO2 systems and fresh water plants
    by booth-at-hplvec.LVLD.HP.COM (George Booth) (Thu, 1 Apr 1993)
  3. CO2, carbonate hardness, etc.
    by (Georg Jander) (4 Apr 93)
  4. Help making a CaCO3 solution
    by (Arch Hughes) (22 Jun 93)
  5. Help making a CaCO3 solution
    by booth-at-hplvec.LVLD.HP.COM (George Booth) (23 Jun 93)
  6. driftwood & pH
    by (Karen A Randall) (Fri, 17 May 1996)
  7. Alkalinity
    by Elizabeth Worobel <eworobe-at-cc.UManitoba.CA> (Sat, 11 Jan 1997)
  8. CaCO3
    by (Wed, 22 Jan 1997)
  9. Re:Calcium supplement
    by (Paul Krombholz) (Mon, 3 Feb 1997)
  10. CaCo (egg shells)
    by krombhol/ (Paul Krombholz) (Sat, 22 Mar 1997)
  11. Water Hardness Measurements
    by Wright Huntley <huntley/> (Thu, 30 Oct 1997)
  12. How do I add Calcium ??
    by George Booth (Sat, 24 Jan 1998)
  13. Co2 and low tapwater pH.
    by Steve Pushak <teban/> (Tue, 24 Feb 1998)
  14. Aquatic Plants Digest V3 #907
    by Paul Sears <psears/> (Mon, 15 Mar 1999)
  15. Calcium
    by "Roger S. Miller" <rgrmill/> (Sun, 11 Apr 1999)
  16. Aquatic Plants Digest V3 #1068
    by George Slusarczuk <yurko/> (Thu, 03 Jun 1999)
  17. Aquatic Plants Digest V3 #900
    by "Andy Dilbert" <ixtapa/> (Thu, 11 Mar 1999)
  18. Adding Calcium (was APD V3 #924
    by George Slusarczuk <yurko/> (Tue, 23 Mar 1999)
  19. Reconstituting RO
    by "Roger S. Miller" <rgrmill/> (Sun, 13 Jun 1999)
  20. Aquatic Plants Digest V3 #1252
    by George Slusarczuk <yurko/> (Thu, 02 Sep 1999)
  21. "Lime"
    by Zxcvbob/ (Fri, 3 Sep 1999)
  22. Aquatic Plants Digest V3 #1125
    by George Booth <booth/> (Thu, 01 Jul 1999)
  23. "Lime"
    by George Slusarczuk <yurko/> (Fri, 03 Sep 1999)
  24. Analysis of calcium carbonate tablet
    by "Roger S. Miller" <rgrmill/> (Thu, 11 Nov 1999)
  25. Aquatic Plants Digest V3 #1126
    by George Slusarczuk <yurko/> (Fri, 02 Jul 1999)
  26. RE:Calcium Carbonate - Aquatic Plants Digest V4 #163
    by "Tom Brennan" <brennans/> (Mon, 20 Mar 2000)
  27. Ca and Mg levels with RO water
    by "Roger S. Miller" <rgrmill/> (Tue, 30 Jan 2001)
  28. calcium tablets
    by "Roger S. Miller" <rgrmill/> (Sat, 17 Feb 2001)
  29. pH of ~ 8 okay?
    by "Roger S. Miller" <rgrmill/> (Sat, 10 Feb 2001)
  30. pH hogwash?
    by Wright Huntley <huntley1/> (Sat, 16 Sep 2000)

[M][some F] Buffering n' pH in marine tanks

by (K. Rogers)
Date: Thu, 11 Jun 1992

OK, this is a sci.aquaria question if ever there were one, but that
group seems to be defunct so here it is in rec.aquaria.

The chemistry question of the day is on buffering, particularly in
saltwater tanks (i.e. mine.)  Like most of you, I'd presume, I've read
over the carbonate buffering sections in books and articles and felt
I've understood the principles, next topic please.  Well, I foolishly
decided to see if I could generate some numbers to see if I really
understood it.  Out came the 15 year old chemistry course book to look
up buffering.  It probably comes as no surprise that I discovered I
don't have a clue how marine tanks maintain their pH at ~8.3.

Actually, you can blaim George Booth (or rather Karla - you all know
that she's the real brains behind the Booth aquaria don't you?  George
just plays around with model choo-choo trainies and lugs water for
her...)  Anyway, you long-timers may remember a series of postings
from him about pH, KH, and CO2 in their plant tanks.  I wanted to do
something like that for my reef tank.

The reactions:

     [H2CO3] <===> [H+] + [HCO3-]   Ka = 4.2x10-7, pKa = 6.4

     [HCO3-] <===> [H+] + [CO3--]   Kb = 4.8x10-11, pKb = 10.3

     And, using 8.3 for a marine pH:  [H+] = 5.0x10-9

Right, plug in the numbers and you get the following ratios:

     [HCO3-]                     [HCO3-]
    --------- = 840             --------- = 104
     [H2CO3]                     [CO3--]

As I see it, both reactions are way out of the buffering region
sitting overwhelmingly towards one side of the dissociation
components.  So how come ocean water sticks at pH 8.3?

As I remember George's postings, they dealt entirely with the carbonic
acid <==> bicarbonate reaction and never wondered far from its
equilibrium point of maximum buffering -at- pH 6.4.  I think I understood
those postings but not my calculations.  If I knew what was going on I
might be able to mix my own Secret Buffering Elixir (TM) but so far I
don't.  I've checked out a couple marine chemistry books but they
haven't helped me any.

Is there a chemist in the house!?

Keith Rogers
Evans & Sutherland Computer Corp.

CO2 systems and fresh water plants

by booth-at-hplvec.LVLD.HP.COM (George Booth)
Date: Thu, 1 Apr 1993

In sci.aquaria, (Shaji Bhaskar) writes:

    >Biogenic decalcification cause the pH to rise according to Dupla and
    >Tetra books.  Tetra gives the reaction as:
    >      Ca(HCO )  - CO   ->  CaCO  +  H O  + CO
    >            3 2     2          3     2       2
    >      ----------------     -----    ---    ----
    >      The plant removes    depos-   extra  used by
    >      CO2 from this side   ited     water  plant
    >The plants will pull CO2 from the bicarbonates leaving CaCO3.  As the CO2
    >is removed, the pH rises. 

Well, based on all the descriptions I've seen, it doesn't make sense to
me either.  They all say the pH goes up.  Maybe someone a long ago said
the pH rises and everyone else is just parroting that (like me :-). 

Perhaps the reaction is not linear in the sense that 1 Ca(HCO3)2 molecule
causes 1 CaCO3 molecule to be deposited.  Since the carbonate/bicarbonate
buffering system is an equilibirium thing, perhaps only 1 CaCO3 gets 
deposited for every 10 CO2's used and the excess carbonate causes the 
pH to rise.  

Maybe someone well versed in chemistry could help out here. 


CO2, carbonate hardness, etc.

by (Georg Jander)
Date: 4 Apr 93

Recently, there was some discussion in this newsgroup about the
following chemical formula:

Ca(HCO3)2 <--> CaCO3 + H2CO3

I would like to add what I know and maybe clarify a few of the 
questions that were raised.
Ca(HCO3)2, actually Ca++ and HCO3- ions, is soluble and is what 
you measure as the carbonate hardness (KH) of your aquarium water.
CaCO3, or calcium carbonate is insoluble and is the main constituent
of limestone.
H2CO3, or carbonic acid is what you get when you dissolve CO2 in 
water by the following formula:

CO2 + H2O <--> H2CO3

Both of these reactions are at equilibrium and reversible.  If you add
components to one side of the reaction, you drive it in the other 
direction.  If you add CO2 to an aquarium that has calcium carbonate
decorations (e.g. dolomite or coral), you will dissolve some of the 
CaCO3 to make Ca(HCO3)2 and thereby increase the hardness of water.
On the other hand, if you have fairly hard water and the CO2 content
is decreased, CaCO3 will precipitate out and H2CO3 is released into
the water until an equilibrium is reached.  In this way, Ca(HCO3)2
acts as a buffer in aquarium water.  Hard water resists pH changes
much better than soft water.

At pH 7.8 or higher most of the CO2 in the aquarium water is in the 
form of Ca(HCO3)2.   Most tropical plants that are commonly grown in ums
aquariums are native to soft, slightly acidic water and can
not utilize carbon dioxide in this form.  They respond to these
conditions by simply stopping to grow.  However, some plants, mainly
those from temperate regions (e.g. Elodea), can continue to grow by 
using energy to drive the reaction Ca(HCO3)2 <--> CaCO3 + H2CO3 to the
right.  H2CO3 is used by the plants and CaCO3 is deposited "in situ"
as a rough white deposit on the leaves of the plants.  This action by
the aquarium plants reduces the hardness and therefore reduces the 
buffering capacity of the water.  If the water was not very hard to
begin with (3 KH, or so), then this can result in a further increase
in the pH.  Naturally, how fast this reaction goes depends on how 
much light energy is available to the aquarium plants.  Under low-
light conditions, a new equilibrium will be established due to CO2
entering the water from the air and from fish, plant and bacterial
respiration.  On the other hand, it is possible for a healthy stand
of Elodea in direct sunlight to raise the pH to lethal levels.

In general, if you notice that white deposits are forming on the leaves 
of your plants, it is a sign that something is wrong.  There is not 
enough CO2 in the water for the plants to grow at the rate they would
like to grow at given the available light energy.  Even those plants that
can use Ca(HCO3)2 do so only because they have to, not because they want 
to.  The best solution to the problem is to increase the CO2 content of 
the water.  Setups for adding CO2 to the water are commercially available 
or can easily be built at home.  If your aquarium does not already have
a lot of fish in it, then increasing the fish population might increase
the CO2 level.  A well-planted 25 gallon tank needs about 1 gram of CO2
per day.  A typical neon tetra produces about 0.01 gram of CO2 per day.
Larger fish obviously produce proportionally more CO2.  Another option
might be to reduce the aeration.  In a heavily aerated tank, the CO2
produced by respiration is rapidly shunted off into the air, leaving a
CO2 concentration of about 0.5 milligrams/liter, which is too low for 
optimal plant growth.  In an aquarium that is heavily planted and which
is not grossly overpopulated with fish, aeration is not really 

Georg Jander         

Help making a CaCO3 solution

by (Arch Hughes)
Date: 22 Jun 93

In article <>, (ROBERT MONTGOMERY) writes:
>       Good Afternoon
>       I was wondering if the net could help in makeing a CaC03 solution I can
>         add to my African tank to help bring up the hardness. I know one 
>       can be purchased but I was wondering how I could produce this 
>       stuff myself. 
>         Thanks in Advance
>         Robert Montgomery

I've used the "Nasco Science" catalog to purchase chemicals.  They
list CaCO3, light ppt. powder, lab at 100g for $5.50 and 500g for
$9.60.  Their toll free number is 1-800-558-9595.

When I've order some chemicals, they won't take the order over the
phone.  I had to fill out the order form and send it in.  They
indicated that they didn't want to deal with individuals, probably for
either first or second hand liability issues (a guess on my part).  I
included a written and signed statement accepting all responsibility
for the proper use, storage, and disposal of said chemicals.  (I
ordered 500g of Ca(OH)2 (reagent grade) to make limewater.  I wish I'd
have ordered just 100g, becasue 500g will last me about 4 lifetimes!)

Even if you don't want chemicals, this is a great catalog.  It's
got just about everything the high school science lab could want.
I've gotten beakers for handling acids and reactivating cupri-sorb,
and have gotten prepared lab slides for my son.  Need a scale for your
archeological field work and weighing coins?  (Enough shameless
promotion...I don't get a kickback, I just like to grovel through
catalogs like this and think of all the fun I could have with the

Hope there's something helpful in the above.  8-)

o o|  Arch Hughes, HyperDesk Corp.        Phone   508-366-5050 x103
o o|  Suite 300, 2000 West Park Dr.       Fax     508-898-3841
---+  Westboro, MA   01581                E-Mail

Help making a CaCO3 solution

by booth-at-hplvec.LVLD.HP.COM (George Booth)
Date: 23 Jun 93

In rec.aquaria, (Arch Hughes) writes:

    When I've order some chemicals, they won't take the order over the
    phone.  I had to fill out the order form and send it in.  They
    indicated that they didn't want to deal with individuals, probably for
    either first or second hand liability issues (a guess on my part).  I
    included a written and signed statement accepting all responsibility
    for the proper use, storage, and disposal of said chemicals.  (I

For much better service, try Hach Chemicals.  They take orders over the
phone, they will take VISA/MC, they ship right away, they also have an 
excellent catalog, they have an excellent water chemistry analysis 
handbook (free) and I guess they don't have as many lawyers working 
for them. 

Hach Company
PO Box 608
Loveland, CO

phone (800) 227-4224
in CO (303) 669-3050
FAX   (303) 669-2932


driftwood & pH

by (Karen A Randall)
Date: Fri, 17 May 1996

Subject: driftwood & pH

Stephen Pushak wrote:

> Anyone care to give us a formula in grams per liter and tsps per
> for an acceptable ratio of sodium bicarbonate and calcium carbon
> when added to distilled water to achieve 1 degree of KH? We shou
> add this to our FAQ. I know it's been mentioned before too.

1/4 tsp of sodium bicarbonate per 50l of water will raise the _KH_ 
one degree. 1/2 tsp. of calcium carbonate per 50l of water will 
raise the _KH and GH_ by one degree.


by Elizabeth Worobel <eworobe-at-cc.UManitoba.CA>
Date: Sat, 11 Jan 1997

> Hi everyone,
> The other day I picked up Tetra's book "Aquariology, Master Volume". In it,
> it states:
> "Sodium Bicarbonate is a pH adjuster rather than a buffer. If added in
> excess to an aquarium, the pH can be elevated to unacceptably high levels.
> A 10% solution of baking soda can safely be used to raise the pH of an
> aquarium.
> ...
> Also, since Sodium Bicarbonate by itself is not a buffer, the desired pH
> may not hold for very long."
> So, who's right? Or am I confusing KH (Carbonate Hardness) and Alkalinity
> (Acid Binding Capacity)? Am I totally confused yet????

George, of course, is correct. As usual the so called aquarium 'experts' 
havent got a clue. Sodium bicarbonate adds inorganic carbon to the water. 
(HCO3). The inorganic carbon equilibrium CO2/HCO3/CO3 is the MAIN 
buffering system in fresh water, so if you add more bicarbonate then you 
increase the buffering capacity of the system. End of story!
The best part of adding sodium bicarbonate is that hardness is completely 
On this list we have agreed that KH and alkalinity are synonymous. In 
actual fact KH is that portion of the alkalinity whose charge is balanced 
by divalent cations such as Ca and Mg ... in other words KH is a measure 
of hardness and has nothing to do with total alkalinity (since charge can 
be balanced by any number of cations).

> I DON'T want to use phoshate buffers and any product which doesn't list
> it's contents makes me nervous. 

Excellent strategy.
> I have a bottle of Seachem Reef Builder, which I use for my marine tank.
> Would it work (in small quantities)? The label states that it will raise
> and maintain alkalinity, restore calcium, magnesium, strontium and trace
> elements. It claims to not directly alter the pH of the water and the
> contents are listed as Sodium, Magnesium, Calcium, Strontium and Potassium
> salts of Carbonate, Bicarbonate, Chloride, Sulphate and Borate.
> What do the chemists think? Can this product be used in freshwater tanks
> (in appropriately smaller quantities) to increase the Alkalinity of the
> water while leaving the GH alone (or at least at a low level)? If not, what
> can be used (other than Dupla's KH builder tablets) to accomplish this
> task?

This is not an appropriate product. It contains divalent cations which 
will increase your hardness (GH). It also contains carbonate and 
bicarbonate so it WILL increase your pH. George's advice (which I 
snipped) is still the best ... to increase pH stability but not hardness, 
add sodium bicarbonate to your tank water.



Date: Wed, 22 Jan 1997

>From: Erik Olson <(e-mail)>

>Actually, I was being a little TUM-in-cheek on that one.  When I was
>desparately searching for CaCO3, I considered this, but I just don't trust
>it.  Call up Hach chemical & get some CaCO3, and use baking soda while you
>wait for it to arrive. :)

Tums definately contain sugar. If you need CaCO3 in a hurry you can buy
pure CaCO3 tablets or caplets in bottles at the drug store. It is not
expensive. I crush the tablets and mix them with some tank water and add
the resulting "slurry"/"suspension" whatever, to the tank. 2 large caplets
= about 1 teaspoon.

in Vancouver

Re:Calcium supplement

by (Paul Krombholz)
Date: Mon, 3 Feb 1997

>From: Thomas Price <>
>Date: Sun, 2 Feb 1997 13:08:15 -0800 (PST)
>Subject: Calcium supplement
>Does anyone add calcium to their tanks?  I think my tank might have a
>calcium deficiency, since the local water is very soft, and my amazon
>sword is putting out leaves that are somewhat stunted and mishshapen,
>but otherwise normal.  I want to add a little calcium, but really don't
>want to increase the KH using carbonate.  I have thought about
>adding some calcium chloride that I have, or maybe some eggshells.  Does
>anyone know what calcium chloride would do, or what form the calcium is in
Calcium chloride will increase your general hardness,(GH) but should have
little effect on your carbonate hardness (KH).  Egg shells should be soaked
in water for two days with several water changes to soak away all the
albumen before adding to tank.  They dissolve very slowly, but should add
to GH and KH a bit.  They are mostly calcium carbonate.  There may be a
little magnesium in them, but not much.  Another way to add calcium is to
put in some ground limestone.  I recently got a 50 lb bag, the smallest
size available at my local garden store, for less than $2.00.  A somewhat
quicker way to add calcium is to add lime, (Ca(OH)2).  I have made cautious
additions of lime, such as 1/4 teaspoon in a 15 gallon tank, and have not
seen any effect on the pH, and it all seems to dissolve in 4 or 5 days.

My tapwater at school comes out of the tap with a pH of 8.5 and it has 9
german degrees of KH, but only 0 or 1 degree of GH, according to my Tetra
hardness test kit.  Why 0 or 1?  The very first drop gives the green end
point color, and so there could be anywhere from no calcium/magnesium to
only enough to be titrated up by the first drop.  Anyway, it is odd
tapwater, and I often wonder if the College is putting sodium bicarbonate
in it or whether it comes out of the ground that way.

Paul Krombholz                  Tougaloo College, Tougaloo, MS  39174
In warm, humid Jackson, Mississippi where the plants are beginning to think
that winter is over.

CaCo (egg shells)

by krombhol/ (Paul Krombholz)
Date: Sat, 22 Mar 1997

>From: Miles Morrissey <>

>              Is calcium carbonate egg shells?  If I were to use a
>mortise and pestle to grind them into a powder would this work as a
>source of CaCo.  Secondly, adding a generic form of tums (which is what I
>use now) Th CaCo does cloud the water some but settles out in a matter of
>an hour or so.  I've been assuming that it settles onto and into the
>gravel where is slowly dissolves as well as settles into the gravel to be
>used by the roots after some time.  Is this accurate?

Yes, egg shells are mostly calcium carbonate.  I have ground them up with a
morter and pestle into a fine powder and dispersed them into an aquarium,
and, yes, they do dissolve slowly, but fast enough, by my observations, to
supply the plants and snails with the calcium they need.  Egg shells also
have organic matter in them.  I once tried heating them in a ceramic
crucible with a bunsen burner, and they turned dark, and then white, again,
as the organic matter became charcoal and then oxidized.  This heating also
drives off water and CO2, leaving calcium oxide.  When calcium oxide is put
in water it becomes calcium hydroxide, which is more soluble than calcium
carbonate, although still not very soluble.  Carbon dioxide in the water
reacts with the calcium hydroxide to produce calcium carbonate, some of
which can react with more CO2 to become calcium bicarbonate, which is quite
soluble.  In summary, the solubility of calcium carbonate is quite low, and
the solubility of calcium hydroxide is a little less low.  If you want to
add calcium hydroxide, you can add small amounts of lime without worrying
that it will make your tank highly alkaline.  By small amounts, I mean
around 1/4 teaspoon in a fifteen gallon tank.

Paul Krombholz                  Tougaloo College, Tougaloo, MS  39174

Water Hardness Measurements

by Wright Huntley <huntley/>
Date: Thu, 30 Oct 1997
To: apisto/ wrote:
> Wright writes:
> <<  KH is
> < carbonate, or temporary hardness. >>
> >>
> If it is "temporary" hardness, where does it go?  I can't imagine calcium
> carbonate or magnesium carbonate just evaporating.  Or is cabonate hardness
> not what I think it is?

CaCO3 easily breaks down to relatively insoluble CaO, precipitated, and
CO2, which is given off to the air. That's why it is called "temporary"
AFAIK. Essentially it becomes "hard water" scale, and no carbonate ions
are left behind.


Wright Huntley, Fremont CA, USA, 510 494-8679
"Subvert the dominant paradigm!"

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How do I add Calcium ??

by George Booth
Date: Sat, 24 Jan 1998
Newsgroup: rec.aquaria.freshwater.plants

Andy Moore wrote:
> Lst night I `disolved` 

NO, NO!  You need to "dissolve" it!  "Disolving" is something else
entirely.  <g>  Sorry, I'm feeling frisky. 

> I stirred it up again and left it overnight. Next morning - fairly
> clear mixture with still loads of powder sat at the bottom of the
> bowl. There is no way that it can be disolved or am I missing
> something ??

Once you have a milky misture, add it to the aquarium.  The CO2 levels
you have due to injection (right?) will help the rest dissolve. In a
tank without a trickle filter, we pour the milky mixture along the back
of the tank.  Some may settle on leaves but it should clear up
overnight. If you have CO2 injection.

What form of CaCO3 do you use.  We buy reagent grade from a chemical
supply house. 


Co2 and low tapwater pH.

by Steve Pushak <teban/>
Date: Tue, 24 Feb 1998
Newsgroup: rec.aquaria.freshwater.plants

David S. Hooper wrote:
> Thanks Ric.  What about the issue raised by Erik concerning salt production
> when using both sodium bicarbonate and calcium chloride?  Maybe I'm better
> off living with a GH that is as close to zero as I can measure.

No!! You need fairly large amounts of Calcium, Potassium, Magnesium and
Sulfer (in order of amount needed). If your tap water is soft or you use
RO water you must add these minerals for your aquarium plants especially
under good growing conditions! You also need Nitrogen and Phosphrus (in
lesser amount) or you'll get low growth and/or yellowish plants. Check
out the how-to article on my web page which describes a simple method to
supply all these minerals as well as trace minerals like iron.

After you're finished adding the minerals, your aquarium water should
have a GH of 2 or more. By the way, for the majority of aquatic plants,
hard water is fine. Some PREFER hard water.
Steve Pushak 

Visit "Steve's Aquatic Page"
 for lots of pics, tips and links for aquatic gardening

Aquatic Gardeners Association

Aquatic Plants Digest V3 #907

by Paul Sears <psears/>
Date: Mon, 15 Mar 1999

> From:
> Subject: Boiling water
> I was always under the impression that boiling water would increase
> the hardness of the water (both DH and GH) because as the water is
> boiled, it evaporates.  

	Boiling water does reduce teporary (carbonate) hardness.  That is why
is is called "temporary".  Boiling drives off dissolved CO2, displacing
the equilibrium:

	2HCO3-  <->  H20 + CO2 + CO3--

to the right.  Calcium carbonate (as opposed to bicarbonate) has a very low
solubility product in water, so the CaCO3 comes out of solution.  If you
want it to _stay_ out of solution, you have to separate the water and the 
CaCO3 before the CO2 comes back after the water cools.

	The KH and GH will be reduced by the same amount, and if the
GH was > the KH to start with, I think the KH can be reduced to a very
low value.  You don't have to boil off a significant amount of the water
to do this, just enough to get rid of the CO2, which has low solubility
at high temperature.

- -- 
Paul Sears        Ottawa, Canada


by "Roger S. Miller" <rgrmill/>
Date: Sun, 11 Apr 1999

I don't recall that anyone responded to this, so I thought I would.

Back on Friday, Christine M wrote:

> I have come to the conclusion that I need to supplement my tank with 
> calcium.  In particular, I am having a terrible time growing regular 
> old swords.  Nearly everthing else thrives.

A while back someone asked about what plants are good indicators for
different nutrient problems.  As near as I can tell "regular old swords"
(E. amazonicus or E. bleheri) are a good indicator for low calcium.  They
seem to show the symptoms before anything else.

> Currently I mix my water from RO with RO Right (or something like it), 
> as well as Baking soda and Epsom salts (about 1.5 tsp of each per 30 
> gal/US).

> Since the goal is very soft water, I would rather not raise the GH 
> much, and I think I need the Mg in the epsom salt, so I was hoping to 
> replace the baking soda with calcium carbonate, which, if I understand 
> the chemistry correctly, would allow me to raise the KH without 
> raising the permanent hardness much.

Calcium carbonate raises both general hardness and alkalinity (KH).  I'm
not sure what you are referring to as "permanent hardness".  The general
hardness added by calcium carbonate is entirely temporary hardness, but
the difference between permanent and temporary hardness is trivial
unless you're going to boil the water.

Don't keep the water soft for the sake of your plants.

> Does anyone know of a source of calcium carbonate?  Would, for 
> example, one of the reef calcium supplements serve this purpose?

Limestone and/or dolomite chips sold in home centers and nurseries are a
source of calcium carbonate.  Dolomite chips also provide magnesium.  
Shells are also a source of calcium carbonate, and oyster shells are sold
as a dietary supplement for not much money.  If you use a dietary
supplement, then read the label carefully.  The supplements often come
with a lot of things, like binders, colors and flavoring that you may not
want.  The cheapest brands might carry the fewest extras

Chips can be put into a filter, or dumped into the tank.  Shells can be
placed in the tank, and the pills can be ground up and slowly dissolved.
It's probably easier to control the result by using the ground up pills.

Reef calcium supplements, aside from being remarkably expensive, aren't
necessarily calcium carbonate.  They may be calcium hydroxide, calcium
chloride or solutions of either of those.  But should you want to play
with some... I used a reef supplement a few weeks ago to give one of my
tanks a one-time-only shot of calcium.  I wasn't concerned about
alkalinity.  It worked just fine.

Roger Miller

Aquatic Plants Digest V3 #1068

by George Slusarczuk <yurko/>
Date: Thu, 03 Jun 1999

Hello Tom,

You just had to pick a question that does NOT have a clear cut answer!

The *saturation* point is when no more of a substance dissolves, or
rather when the substance in solution is in an equilibrium with the
solid phase, out of solution.

The *solubility* of calcium carbonate [CaCO3] in *pure* water is only
about 17 ppm (i.e. about 1 "German degree"). It is a well known fact,
that calcium BIcarbonate [Ca(HCO3)2] is much more soluble in water than
calcium carbonate. Calcium bicarbonate is unstable, exists only in
solution, one can not isolate it & put in a bottle. The way one prepares
it, is to add CO2 to the water which is in contact with excess solid
CaCO3. The CO2 (actually carbonic acid, H2CO3) reacts with the calcium
carbonate in solution, forming the bicarbonate, and shifts the
equilibrium, allowing more solid calcium carbonate to dissolve... and so

If enough CO2 is present, a lot of CaCO3 can dissolve. My well water has
430 ppm CaCO3 hardness. I have heard of places with REALLY hard water
("liquid rock") with over 1,000 ppm CaCO3. So, depending upon available
CO2, the calcium concentration will vary.

Most solid-liquid reactions are slow. In an aquarium with fish one does
not want to change the water parameters rapidly -- it puts stress on
fish, might even kill them. So, a slow coming to equilibrium, in my
book, is an advantage: Just place some marble chips (in a sock) in your
filter, and forget about it for several days. Take out the sock when you
reach the target hardness -- that's all there is to it!

Adding calcium as CaCO3, vs. CaCl2 or Ca(NO3)2 has the further advantage
that you are also increasing the alkalinity (KH) and *buffering
capacity* -- the ability of the system to resist changes in pH.

If you have further questions, feel free to ask.



> Date: Wed, 2 Jun 1999 17:29:51 -0400
> From: "Tom Brennan" <>
> Subject: Re: was APD V3#1063 & Calcium Deficiency
> George wrote........
>  Mon, 31 May 1999 16:12:40 +0000
> From: George Slusarczuk <>
> Subject: Re: Aquatic Plants Digest V3 #1063
> Hello Ken,
> Calcium chloride works well, but will acidify your water.
> Marble chips (used in landscaping) in the filter will keep calcium
> carbonate at saturation level.
> Dolomite (sometimes used as gardening lime) will also add magnesium to
> the water. Magnesium is needed for chlorophyll formation.
> Best,
> George
> ============================================================
> George/All....
> What is saturation level?  Is this the point where Ca precipitates out of
> solution.  Also I have used "Sweet 'N Grow " Bakers Dolomite - Hy Magnesium,
> Pulverized Lime Stone
> Chemical Analysis:
>                                                        Minimum Percent
> Calcium Carbonate (CaCO3)......................53.5%
> Calcium Oxide (CaO)...............................30.0%
> Magnesium Carbonate (MgCO3).................42.0%
> Magnesium Oxide (MgO)..........................20.0
> Elemental Magnesium (Mg)........................12.1%
> Elemental Calcium (Ca)............................21.4%
> Calcium Carbonate Equivalent (C.C.E.).....105.6%
> and noticed it takes quite some time for the gH/kH to rise maybe days.  I
> thought by injecting Co2 it would devolve faster or almost immediately.  The
> Bakers Dolomite is a very fine powered and seems to dissolve upon slight
> mixing?  Is this what I want to use or should I seek out CaCO3 for kH/gH and
> use baking soda for increasing kH/gH.  By now you should have guess I am not
> a chemist!
> Tom Brennan

Aquatic Plants Digest V3 #900

by "Andy Dilbert" <ixtapa/>
Date: Thu, 11 Mar 1999

Hi James, et al,
A cheap easy source for CaCO3 is in your local winery supply shop...  they
usually sell powered CaCO3 for wine-making.  And since it is for human
consumption, it meets high human food regulations; it will not contain
contaminants that are harmful for your fish!
- -Andy

James Purchase wrote:
>Calcium Carbonate is available from
>any pharmacy (look in the section carrying nutritional supplements). I
>a tablet using a mortar and pestle and then add it to the aquarium to keep
>my Calcium levels up.

Adding Calcium (was APD V3 #924

by George Slusarczuk <yurko/>
Date: Tue, 23 Mar 1999

Hello Bob,

The simplest way is to add CaCl2, obtainable in hardware stores for
de-icing. However, there is a danger that something might have been
added to it. I have seen CaCl2 *flakes* for sale in 5-gal buckets. That
is relatively pure. CaCl2 will lower your pH a little bit.

Dolomite -- CaMg(CO3)2 -- has both calcium and magnesium, so should be
your next choice. It is obtainable in garden stores for liming lawns
(but read the composition, whether it says "dolomite", "dolomitic",

Any strong acid, HCl (masonry), H2SO4 (pools) will do the job of
decomposing the carbonate. Here the problem will be NOT to acidify the
resulting solution too much with excess acid. 

I don't know how to figure out concentrations on something that is only
partially dissolved. What I would do, is make a kind of thin "soup" with
*excess* dolomite, so no excess acid is present. Let it settle overnight
and decant. 

Add a known volume of the supernatant to, say, 1 liter of water and
measure hardness. From that calculate how much "soup" you need for the

DON"T FORGET to change hardness sl-o-o-oowly, over days!

[I know, that you don't need that warning, but all of us sometimes get
overly impatient!  :-) ]



> I am trying to decide how best to add calcium without introducing carbonate
> hardness.  Myy NO3 tests around 10 ppm, so I could go with CaNO3.  Also CaCl
> is an option.  Is either of these available commercially, or do I need to make
> my own with dolomite and the appropriate acid?  If they are available, where
> at?  I could also use sulfuric acid from a swimming pool store.  My fish are
> SA cichlids and tetras, so I have been trying for a soft environment, I think
> maybe just not as soft as I have.  I'll pick up a hardness test tomorrow and
> detirmine GH and Calcium hardness before I start this.  Dosing recommendations
> for a 30 gallon with approximately 25 gallons net?
> Bob Dixon

Reconstituting RO

by "Roger S. Miller" <rgrmill/>
Date: Sun, 13 Jun 1999

At the risk of triggering another (ad nauseum) from the list Mom...

Bob Dixon wrote:


> How about dolomite?  It is available 
> crushed from gardening centers, and if we redirect a small amount of CO2 from 
> our aquaria to our mixing "vats" it should dissolve overnight.  Would it not 
> contain the correct, or close enough to the correct, ratios of Ca, Mg, and 
> CO3?  And would CO2 injection even be necessary to get it dissolved at a 
> reasonable rate if we are preparing our water far enough in advance?

If what you aim to do is add general hardness and alkalinity, then
dolomite is probably a better choice than calcium carbonate.  Ideally, it
provides Ca and Mg in the ratio of 5:3 (by weight) and GH and KH in a 1:1
ratio.  Dolomite is often not pure, and the Ca:Mg ratio will increase if
there is any calcite in the dolomite.  Calcite in the dolomite will not
change the GH:KH ratio.

On the slightly down side, dolomite is a little more difficult to dissolve
than calcium carbonate, and I've never seen it available in nicely
preweighed quantities like calcium carbonate tablets.

The recipe I offered wasn't intended just to increase GH and KH, but to
provide a DIY means of reconstituting RO water to get water that resembles
"normal" fresh water in it composition and provides the nutrients normally
required in fresh water in ratios that should be good for growing plants.

If I lose the epsons salt from the recipe in favor of dolomite for
magnesium and alkalinity then the recipe will need some other source for
sulfate.  I'll also have to drop the baking soda out of the recipe, as
that would not be needed to provide alkalinity, and dropping the baking
soda out would leave sodium out of the recipe.

Sulfate (for sulfur) is used by plants, though not in large amounts.
Sulfate is usually common in fresh water so I'd be surprised if plants are
adapted to scavenge sulfate at low concentrations.

Sodium isn't needed for plant growth as far as I know, but it is pretty
much ubiquitous in natural water and I don't feel real comfortable leaving
it out of the mix.  Animals may very well need it for something or other.
> ------------------------------

Write Huntley wrote:

> >In most parts of the US, the effective way to rebuffer the RO water is by
> >just mixing back in some tap water until the desired hardness/buffering is
> >reached.

This is certainly the easiest way to reconstitute RO water.  It gives you
a mix that is just a diluted version of your tap water.  Usually that's

If your tap water is really bad for growing plants (e.g. sodium too high
compared to Ca, Mg, K) or contains some normal component in very small
amounts (K, for instance) then other chemical additions may still be
necessary.  Without using something else to reconstitute the water you
would just be making the original problems worse.

> ------------------------------

James Purchase wrote:

> Regarding your "recipe" for water:
> > We can do better than that.  Here's a recipe
> >
> > Chemical dose/ dose/ measurement
> > 100 liters 50 gallons unit
> >
> > epson's salt 3.5 6.5 quarter teaspoons
> > calcium carbonate 6 11 600 mg tablets
> > baking soda 4 8 quarter teaspoons
> > potassium chloride 1.5 3 quarter teaspoons
> Is this using 1/4 tablespoon measures? (measuring spoons come in sets - 1/4,
> 1/2, 1 Teaspoon, and 1 Tablespoon)

Mmm.  Looks like your mail client stripped the tabs out of the table. That
certainly makes it harder to read.  There should be four columns.

The doses for epsons salt, baking soda and potassium chloride are cited as
the number of 1/4 teaspoons needed:  3.5 quarter teaspoons (for instance)
is 7/8 of a teaspoon.  8 quarter teaspoons is two teaspoons, and so on.  
I used the 1/4 teaspoon as my measuring unit because Neil did it that way.
It seems to be pretty convenient, though perhaps not the most obvious way
of doing things.

Incidentally, my tap water is far from great for growing plants, so I
already add three chemicals to all the water I put in my tanks; sodium
thiosulfate for dechlorination, potassium chloride and epsons salt.  The
difference between my normal procedure and DIY RO-water reconstitution
(which requires only 4 major chemicals) is so small that I wouldn't need
to be very upset about the commercial alternatives before deciding to do
it all myself.

But I'm like that.

Roger Miller

Aquatic Plants Digest V3 #1252

by George Slusarczuk <yurko/>
Date: Thu, 02 Sep 1999

Hello Michael,

> Alternatively, I've read here that dolomite chips contains Ca and Mg, making
> it a good candidate for GH adjustment - where does one look for such an
> item?

Look for "lime" in garden/landscaping stores. It usually is crushed

Also in these stores you can get marble chips -- almost pure CaCO3.




by Zxcvbob/
Date: Fri, 3 Sep 1999

George sez:
> Look for "lime" in garden/landscaping stores. It usually is crushed
>  dolomite. 

Careful, "lime" is calcium hydroxide, made by hydrating calcium oxide.  
"Limestone" is calcium carbonate.


Aquatic Plants Digest V3 #1125

by George Booth <booth/>
Date: Thu, 01 Jul 1999

>Date: Thu, 1 Jul 1999 01:28:35 -0700
>From: "Mortimer Snerd" <>
>Subject: Re: GH and kH from Calcium Hydroxide
>I've not been able to find calcium carbonate in a powdered form locally, and
>am leery of the binders that are used in the tablets found in drug store
>products, so I have been playing with the Ca(OH)2 as a convenient and highly
>soluble substitute.

If you have any homebrewing stores in your area, they sell small quantities
of very fine CaCO3. We tried it and it seems to dissolve easier than CaCO3
from Hach  Chemical (for instance). The homebrew CaCO3 comes in small jars
but the price is about the same. 

George Booth, Ft. Collins, Colorado


by George Slusarczuk <yurko/>
Date: Fri, 03 Sep 1999

Hello Bob,

Technically you are correct. 

The package in garden/landscaping stores usually just says "lime" or
"garden lime". In my neck of the woods, underneath it it also says
"dolomite", albeit in small print.



> George sez:
> > Look for "lime" in garden/landscaping stores. It usually is crushed
> >  dolomite.
> Careful, "lime" is calcium hydroxide, made by hydrating calcium oxide.
> "Limestone" is calcium carbonate.
> bob

Analysis of calcium carbonate tablet

by "Roger S. Miller" <rgrmill/>
Date: Thu, 11 Nov 1999

On Thu, 11 Nov 1999, Tom Bates wrote:

> A friend of mine (not in the APD) is attempting reconstitute RO water for
> aquarium use. She went to her local pharmacy and got CaCO3 tablets and,
> after reading the ingredients, is wondering if there is anything in this
> tablet that would be unsafe for aquarium use. Not being a chemist myself, I
> thought I would ask the members of APD. Other than Calcium or Calcium
> Carbonate, here are the ingredients as listed on the bottle. Percentages not
> listed.

Tell your friend to keep the calcium supplement for herself and go back to
buy one that is as nearly pure calcium carbonate as she can find.  I took
a quick trip to the grocery store and found one brand (Sundown) that was
pure calcium carbonate and a second brand (Nature's Bounty) that was pure
calcium carbonate, but coated.

Roger Miller

Aquatic Plants Digest V3 #1126

by George Slusarczuk <yurko/>
Date: Fri, 02 Jul 1999


If you don't mind a bit of magnesium with your calcium (actually plants
*need* magnesium) "garden lime" used on lawns is a good source. At
~$3.00 per 40-lbs bag it can not be beat. What if some of it doesn't
dissolve readily? Lot of it does, the rest you just throw out.



> Date: Thu, 1 Jul 1999 12:59:35 -0700
> From: "Deborah Burt" <>
> Subject: Re: calcium carbonate source
> Hello all!
>  I have recently joined the list, and want to express a big THANK YOU to all
> who have helped educate me in the care of aquatic plants. I now have 3 tanks
> going, have built my own CO2 reactor and am having a lot of fun!
>  Justin was asking about a source of calcium carbonate. Being a reptile
> breeder and keeper, I thought about the calcium supplement I use for my
> lizards. It isn't cheap (about $7 for 4.1 oz/116 gm) but it is pure calcium
> carbonate in very fine powder form. Look for Rep-Cal (NOT Repti-cal) without
> Vitamin D3 at the local pet store. I don't know if the D3 would cause any
> trouble (I would think not)but no reason to add anything extra if you don't
> have too.
> Deb
> (In Renton, WA where the sun is out again!)
> Justin wrote in APD #1125
> <cut>
> >I've not been able to find calcium carbonate in a powdered form locally,
> and
> >am leery of the binders that are used in the tablets found in drug store
> >products,
> <cut>

RE:Calcium Carbonate - Aquatic Plants Digest V4 #163

by "Tom Brennan" <brennans/>
Date: Mon, 20 Mar 2000


I use to order ACS grade CaCO3 from Hach (#12001, 454g=$40 -or - #12014,
113g=$19, see em at:  Go into the "Product Ordering" section,
"Browse Catalog" and search under the "Product Type" drop-down box and
choose "Chemicals and Reagents", this page takes a while to load then find
"Calcium Carbonate" farther down on the page.  This was a pain to find my
first time on their page!

This got expensive and I have been experimenting with sea shells, garden
lime, and lime pellets, they are much cheaper but take for time to dissolve.
I use good-ole backing soda to boost alkalinity/buffering/kH.  Both work
well. Actually I keep quite a few shells in on of my Magnum 350s and add
lime or dissolved lime pellets at water changes to get my water up to
4kH/3gH.  I also have some Calcium Hydroxide (SeaChem Reef Kalkwasser) but
found out quick this rapidly sucks all the PH out of your water and you pH
skyrockets immediately!  Someone mention on the list that I could bubble Co2
into a mixture of the Calcium Hydroxide and water and precipitate the CaCO3
out, too much trouble.  I may add a 1/4 tsp sometimes while adding lime and
don't see that much of a jump in pH.  As you guessed it, I am not a chemist!

Comments, suggestions on what I am doing are welcome.

> Date: Sun, 19 Mar 2000 03:17:48 -0800
> From:
> Subject: Calcium Carbonate
> Any advice on where I could get this chemical? Currently I'm
> using the Dupla KH + GH tablets to alter my water hardness but
> these are damn expensive to buy. Is it like Sodium Carbonite
> where I can just pick some up from the local supermarket?
> Thanks,
> Gordon
> or via FTP to in /pub/aquaria/aquatic-plants.

Ca and Mg levels with RO water

by "Roger S. Miller" <rgrmill/>
Date: Tue, 30 Jan 2001

On Tue, 30 Jan 2001, Jay Reeves wrote:

> What are people using RO water remineralizing and increasing KH  with?
> I have been using Kent RO Right to remineralize and Kent pH Stable to
> add KH.  Probably not a problem with the RO Right, however, pH Stable
> contains carbonic acid monosodium salts.  I have been adding baking soda
> as well to get to 3-4 KH.

"carbonic acid monosodium salts"?  I think that *is* baking soda.  Of
course, Kent couldn't just say that.

> In looking over past postings I saw
> references to adding CaCo3 (calcium carbonate?) to increase hardness and
> that this available from the drug store.  What product?

Calcium pills from the grocery store (read the ingredients, get the one
that comes closest to pure CaCO3 -- it's usually a cheap brand), marble
chips from a nursery or oyster shell.  They all work.

> Minneapolis gets water
> from the Mississippi River whereas suburban communities have well
> water.  Water quality, not economics, is the determining factor in this
> disparity.  I will continue to consider tap water, but plan on
> continuing use of RO until I get a better handle on things.

My bet is that Minneapolis tap water is fine and that RO water is a waste
of your time and money.

Roger Miller

calcium tablets

by "Roger S. Miller" <rgrmill/>
Date: Sat, 17 Feb 2001

A reader previously wrote:

> >What about blackboard chalk pieces ?

Blackboard chalk was traditionally pure CaCO3.  Two or three years ago I
suggested chalk as a source for calcium and Paul Sears pointed out that
chalk these days isn't always CaCO3.  I checked what I had; it wasn't. 
Check yours before you try using it.  If it is CaCO3 then it should fizz
when hit with a drop of vinegar.

If you find some blackboard chalk that is CaCO3 then it should be a
useful source of calcium.

Roger Miller

pH of ~ 8 okay?

by "Roger S. Miller" <rgrmill/>
Date: Sat, 10 Feb 2001

Nathan Wittmaier wrote:

> Hullo. I know that pH has been discussed quite a bit, but I was wondering if
> a pH in the range of 7.8 to 8.2 is suitable in general or if certain plants
> would prefer it.

I don't think there's very much of a direct effect of pH on plants. 
Mostly high pH is a problem because it implies low CO2.  Some plants can
do very well under those conditions - Vallisneria comes to mind as a
good example.  If you want to grow plants under low-CO2, high-pH
conditions then I think you have two possible approaches.

With bright artificial light or sunlight a few plants will do very well
using bicarbonate as their carbon source.  You probably will find that
only one or two species of plants will coexist under those conditions,
because there is very intense competition and plants that are less
well-adapted to those conditions will die.

With dim light you can grow a larger variety of slow-growing plants that
can subsist on low CO2 supplies.  Plants grown under low light w/o CO2
generally aren't very robust; they respond poorly to temporarily bad
conditions and they don't recover very well from damage (like pruning or
transplanting).  Plants grow slowly under those conditions, so they
won't do much to control the level of nutrients (nitrate, for instance)
in the water.  Some algaes (BBA comes to mind) grow relatively well
under these conditions.

> According to the local water department, that is the pH out
> of the tap. The little color-comparison pH test kit I have only goes up to
> 7.4, and my reading from tank water seems to be above that. I don't
> supplement with CO2 and don't plan to. Should I make efforts to adjust or
> just not worry about it?

Don't use chemical additions to adjust the pH of your water -- they tend
to cause more problems then they solve.  You can mix your water with RO
or distilled water to get a lower pH, and reduce aeration or surface
turbulence to retain more CO2.

Roger Miller

pH hogwash?

by Wright Huntley <huntley1/>
Date: Sat, 16 Sep 2000

Hi folks,

Recent threads, mostly on CO2 (do we even have any others?) have shown some
attitudes toward pH that are, IMHO, quite unwarranted. I intend to make a
few blanket statements, based on my experience, that I'm prepared to defend.

Unfortunately, many books and LFS clerks have wildly *different* opinions,
so it behooves us to seek the truth, wherever we can find it. That said,
here goes:

1) Fish are remarkably insensitive to pH alone between about 4 and 10, and
they don't react to it unless some secondary factor is present, that
altering the pH changes -- like converting ammonium to ammonia. [pH below 3
can maybe kill some fish. I accidentally did it to some baby Cories, once.

2) Plants may have slightly higher sensitivity to pH, tds, hardness, etc.,
but the boundaries are probably wider than we usually hear about here.

3) There simply is no such thing as "pH shock." The fish can't feel or taste
it, and I routinely subject delicate fish to abrupt changes of 2 or more
points. In the Scheel _Atlas of Killifishes of The Old World_  he claims
sudden swings of over 3 points have no effect. An unfortunate connection
between alkalinity, tds (osmotic pressure) and pH started the myths, and
many authors have ignorantly propagated them to this day.

[Don't subject your fish to sudden large changes in dissolved solids (tds)
for that *can* kill them for sure. They need time to adjust their osmotic
pressure regulators.]

4 ) pH is a useful thing to measure, along with alkalinity (unfortunately
confused with hardness by calling it "carbonate hardness") primarily to use
the CO2 concentration equations or charts to set the CO2 level for proper
plant nutrition.

[Trying to otherwise adjust the pH chemically, to some false ideal, just
creates a chemical soup and *more* stress on the fish, and even more lush
algae, under most circumstances.]

Keeping the pH from going low in the presence of nitrites and heavy metals,
or high if a lot of ammonia is present, is a prudent thing to do to keep
from simply poisoning your fish with these pH-related toxins. Good
water-change practices and heavy planting virtually eliminates these things
as considerations. 

[I learned the hard way to keep lead plant anchors out of low-pH, salty

Neither fish nor plants really like tds shock, for the cells have to adjust
to maintain proper concentrations of various salts in the internal fluids. I
am observing that I kill less "wanted" organisms by paying attention to tds
change, than I ever did when I thought pH was some kind of magical thing.
YMMV, but I'll still put up the old flame shield, just out of habit. (^_^)


- -- 
Wright Huntley, Fremont CA, USA, 510 494-8679  huntleyone at home dot com

"People constantly speak of 'the government' doing this or that, as they
might speak of God doing it. But the government is really nothing but a 
group of men, and usually they are very inferior men." --H. L. Mencken

               *** ***

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