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  1. Calcium supplementation(M)
    by mar/ (Mark A. Rosenstein) (Fri, 20 Mar 1992)
  2. Calcium supplementation(M)
    by mar/ (Mark A. Rosenstein) (Wed, 25 Mar 1992)
  3. [M] Cheap Calcium?
    by efang/ (6 Apr 92)
  4. (M) T.clam eat too much calcium
    by patti/hosehead (Patti Beadles) (Mon, 18 May 1992)
  5. More calcium wars (long!)
    by patti/ (Patti Beadles) (Tue, 19 May 1992)
  6. Calcium level
    by laurence/ (Dustin Lee Laurence) (28 Jul 1993)
  7. Calcium level
    by kvk/ (Ken Koellner) (28 Jul 1993)
  8. Test Kit Information and Others
    by ahughes/ (Arch Hughes) (5 Nov 92)
    by cb77/ (Craig Bingman) (14 Feb 1994)

Calcium supplementation(M)

by mar/ (Mark A. Rosenstein)
Date: Fri, 20 Mar 1992
Newsgroup: rec.aquaria

It's important to keep the calcium levels up in a reef tank for several
reasons: besides to obvious supply of calcium for stony corals and shell
building mollusks, it also promotes the growth of coraline alge and certain
types of macro-alge.  With a decent calcium supply, you may discover
juvenile corals growing from your live rocks.

A good target to aim for is 400 ppm calcium.  Depending on how you add it,
you may or may not need to actually measure the levels.  If you are going 
to buy a calcium test kit, people on the net seem less pleased with the
LaMotte kit and suggest the Hach kit instead.

The most common way to add calcium is through Kalkwasser, or limewater.
You can buy this pre-mixed, but it's pretty expensive that way.  You can
also mix it yourself with a mix sold by Kent Marine, Theil, or just go to
a chemical supply house and get Calcium Hydroxide Ca(OH)2.  You mix it to
saturation (about a tablespoon per gallon), letting any extra settle to the
bottom.  How much do you add?  Not too much at one time, as it will upset the
pH and buffering system, but I've heard of people using as much as all of
their top-off water being kalkwasser.  I add about a pint a day to my 30G

Kalkwasser will keep the calcium level constant, or slowly increase it.
If you want to raise the level faster, there are more concentrated additives
available.  You can get them from Kent Marine, CoraLife, Theil, SeaChem,
and probably others.  If you want to do it yourself, use calcium chloride,
and calculate a dosage that won't raise it by more than 10ppm per day.
Some of the commercially prepared additives are chelated, which makes them
safer to use, but they may not be detectable by your calcium test kit.

Finally, there are other additives that are probably a good idea to use
with calcium.  If you are adding a lot of kalkwasser, you may need to add
a buffer to boost the carbonate hardness.  Most creatures that use calcium
require strontium as a vitamin while they are fixing the calcium.  This is
commonly added as Theil's KSM or similar products from other manufacturers.


Calcium supplementation(M)

by mar/ (Mark A. Rosenstein)
Date: Wed, 25 Mar 1992
Newsgroup: rec.aquaria

In some sense, the amount of Ca(OH) you add to the water to make kalkwasser
doesn't matter.  For it to be effective, you want to bring the solution to
saturation.  I'm not sure exactly what point is saturation; I always add more
than necessary.  Any extra that you add will just settle to the bottom.  
Careful pouring will leave it on the bottom of the container.  When you use
up most of the kalkwasser, just add more fresh water and see if all of the
precipitate dissolves.  If it does, add a little more powder to keep the solution
at saturation.

So to the person who adds only 1/4 teaspoon and doesn't get any precipitate,
you are probably not getting a saturated solution.  I add a lot more than that
(about 1 tablespoon) but a lot of it doesn't dissolve.  One other thing to keep
in mind is that after a while, you should discard the stuff from the bottom
of the bottle.  Some of it will have turned into CaO3 and is no longer useful.

[M] Cheap Calcium?

by efang/
Date: 6 Apr 92
Newsgroup: rec.aquaria

In article <>, (Anthony Tse) writes:
> In article <> (Kevin N. Carpenter) writes:
>>buffering to counter the pH of the limewater.  Furthermore, the addition
>>of Calcium Hydroxide (lime) is desirable over the addition of Calcium
>>Chloride since no non-calcium additions would be added to the water (Calcium
>>Chloride would cause an eventual buildup of chloride ions, much like the

How much calcium are you going to add anyway? This will only be true if you are
going to add CaCl2 in amounts comparable to the salt in your tank, which is on
the order of pounds. Even if you are going to add as much as a tenth of the
weight of salt, water changes will keep bringing the concentration down.
Do the math.

>>buildup of sodium ions that would happen if I added sodium bicarb).
> I am not at all sure if this is the case.  Salt is Sodium Chloride, so
> what's wrong with calcium chloride.  Not to mention the quantity you
> are adding.  My problem with adding calcium chloride is with KH
> dropping, I am not sure is it with CaCl2 or do I just have too much
> stony & clams that uses carbonate up real quick.  I have to add
> 1 table spoon of Sodium carbonate and 2 table spoon of Sodium
> Bicarbonate every week to keep my KH at around 8.

The problem is probably that CaCO3 has a very low solubility (.002g/100cc)
compared to CaCl2 (159g/100cc)! This is ~5 orders of magnitude! I would guess
that the amount of Ca ions that you add is high enough to force some of the CO3
ions to precipitate out with the excess Ca. Maybe someone can look into
addition of CaCO3 instead- it has a much lower solubility but you will not have
to worry so much about your KH.A mixture of both CaCl2 and CaCO3 should be able
to add more Ca ions in the same amount of solution than plain CaCO3. You have
to work out the stoichiometry, though. I don't have time right now. Spent my
weekend in Palm Springs and didn't get any work done. Now I pay.....

> -Anthony

Eric Fang

(M) T.clam eat too much calcium

by patti/hosehead (Patti Beadles)
Date: Mon, 18 May 1992
Newsgroup: sci.aquaria,alt.aquaria,rec.aquaria (Greg Smith) writes:
>patti-at-hosehead (Patti Beadles) writes...
(other attributions lost)

>>>>What are the effects of extra clorine ions ?
>>>	None what so ever.
>>I'm not convinced of this.  I saw some numbers that indicated that the use
>>of CaCl2 could pretty quickly cause an ionic imbalance.

>I have to disagree with you on this one Patti.  I don't know where you saw
>your numbers but they are most likely wrong.  When adding CaCl2 in quantities
>to maintain Ca at 400ppm compared to chlorine which is at 19000 ppm and 
>performing regular water changes to the tune of 10 percent per month.  You
>will never change the chlorine concentration by more than a few percent.  You
>will find variations larger than that between different brands of sea salt and
>possibily between different batches of the same brand.

First a quickie correction:  It's clorine gas, but chloriDe ions.

I've been doing some back-of-the-envelope (actually Post-It(TM) note)
calculations.  I make a lot of assumptions in this, but I don't think
any of them are unreasonable.  The numbers are definitely rough, and I
haven't doublechecked them.

Start with a mythical 100l (roughly 25-gallon) tank.  Assume that the
starting Ca++ concentration is 400 mg/l.  Assume, also, that after one
month, the Ca++ concentration falls to 250 mg/l.

Assuming no loss, it will take 15g of Ca++ to raise the concentration back
to 400 mg/l.  That means it will take 41.6g of CaCl2 (anhydrous, assuming
100% purity.)  26.6 grams of this is Cl-.  That means the Cl- concentration
has been raised by 266 mg/l.

In reality, a lot of the Ca++ is lost to precipitation when CaCl2 is used.
My experience has shown that you'll be lucky if half of the Ca++ remains
in solution.  Assume we're lucky; the Cl- concentration has been raised by
532 mg/l to 19,532 mg/l.

Now along comes a 10% water change with water that has a chloride level
of 19,000 mg/l.  The tank will have a final Cl- concentration of 19,479
mg/l, or 2.5% higher than normal.  No big deal, yet.

Next month, the same thing happens, only this time we're starting with
water that has 19,497 mg/l of Cl-.  When we add an extra 532 mg/l and then
do a 10% water change, the result is a level of 19,910 mg/l, or roughly
4.8% higher than normal.

The third month gets us a concentration of 20,300 mg/l, or 6.8% higher
than normal.  Month four gets us 20,650 mg/l, or 8.7% higher than normal.
You can carry these calculations out as far as you'd like.

The percentages are the same for any size tank (100l is easy to work with
for computing mg/l, which is why I chose it.)  Eventually you get to some
pretty big numbers.

What I don't know is what amount of variation is acceptable.  My personal
feeling is that 10% is too much, but I have nothing to back this up with.
And after six months of this ritual, you've reached a 12% higher than normal

Bottom line:  constant additions of large amounts of CaCl2 will definitely
have a significant impact on the chemistry of the tank.  Whether or not
this change is detrimental to the life in the tank has not been determined.

Recommendation:  If you want to use CaCl2 as a sole source of calcium
supplementation, I would recommend that you do large water changes at least
twice a year, and preferrably quarterly.  This will help to reduce the
buildup of Cl- ions in the tank.
-- | I don't speak for Intel, nor vice-versa. |
             (503)-696-4358 | A1: Yes, I'm the one with the big fishtank.
or just yell, "Hey, Patti!" | A2: A lot, a lot, yes you can see it sometime.

More calcium wars (long!)

by patti/ (Patti Beadles)
Date: Tue, 19 May 1992
Newsgroup: alt.aquaria,sci.aquaria,rec.aquaria

I received this in the mail from someone today, and thought it was
worth posting (with the author's permission, of course.)  I've edited
out a few irrelevant bits, but it remains intact otherwise.

(begin included article)
Recently on USENET I read the following:

>>If you used the same amount of Calcium in the form of
>>Calcium Hydroxide your pH would eventually skyrocket after the hydroxide 
>>overcame your buffer system and kill everything!

To which you spake to this CaCL2 adding infidel:
>Proof?  Have you ever known of this happening?  I dump a lot of calcium
>hydroxide into my tank, and my pH stays fairly stable.  There are acids
>being produced all the time in a tank.  (I'm not saying it's impossible;
>I'm just wondering if you've ever heard of it.  I have heard multiple
>incidents of problems with CaCl2 overdose, but never Ca(OH)2.  If you know
>of any, I would like to add them to my knowledge base.)

I sadly have no personal experience with reef tanks, although I do find
the subject quite fascinating, and once my Ph.D. in Biochemistry starts
to earn me those Big Bucks, I will no doubt acquire such a multithousand
dollar establishment for wayward corals and giant clams.

Never the less, I thought it is worth noting that the typical reef tank
is in contact with an extraordinarily large reservior of a subsatance
that, when dissolved in water, gives a weakly acidic solution.
The reservior is the atmosphere, and the substance is carbon dioxide.

I would humbly submit that this, in addition to the acid generating
processes within the tank, may act to keep the pH stable, even upon
addition of kalkwasser.  In fact, if I recall correctly, this even
happens when solutions of kalkwasser are allowed to stand in contact
with the atmosphere.  It reacts with CO2 to give calcium carbonate.

I also found the fact that your "alkalinity" or whatever dropped
when you added calcium chloride.  That also might make some sense,
expecially if the Ca++ you are adding is reacting with atmospheric
carbon dioxide.

Ca++  + 2Cl- +   H2CO3   --->  CaCO3 (insol.) + 2Cl- + 2H+

or if you prefer:

Ca++  + 2Cl- +   H2O + CO2   --->  CaCO3 (insol.) + 2Cl- + 2H+ 

Both reactions generate 2 equivalents of acid per equivalent of
Ca++ added.

Now, let's consider what would happen if we added calcium hydroxide

Ca++ + 2OH- + CO2 --->  CaCO3 (insol.) + H2O

Looks like a hell of a lot more stable situation to me.  And I don't think
that it will make any difference if it is a clam or coral laying down the
calcium carbonate, or if it occurs somewhere else in the tank.  Adding
calcium chloride would seem to decrease the pH of the tank, and over
the long haul, calcium hydroxide would not.

But then again, I am simply a humble biochemist, and not a reef tank
keeper.  Perhaps all this has been thrashed to death on USENET, 
maybe not.  If not, you may certainly feel free to post this to 
alt or rec.aquaria.

Craig Bingman

copyright 1992 (craig bingman)
-- | I don't speak for Intel, nor vice-versa. |
             (503)-696-4358 | A1: Yes, I'm the one with the big fishtank.
or just yell, "Hey, Patti!" | A2: A lot, a lot, yes you can see it sometime.

Calcium level

by laurence/ (Dustin Lee Laurence)
Date: 28 Jul 1993
Newsgroup: rec.aquaria (Paul Ko          CSC) writes:

>Hi there!

>I just bought Lamott's Calcium test kit and the Alkalinity test kit. I just
>would like to know what is a good calcium level for a reef tank. (in units
>of ppm).

You need to know if the kit measures ppm Ca++ or ppm equivalent CaCO3.
The HACH kit measures the latter, for example, while all the aquarium
literature I've seen measures the former.  The conversion is easy to
calculate, but the bottom line is that 20 ppm CaCO3 = 8 ppm Ca++.

As for the correct level, seawater is usually said to be around
420 ppm Ca++.  I like to maintain it at about this level.

>Also, how do you convert the Lamotts alkalinity test kits reading in ppm to

I don't remember this conversion factor.

>I think I read somewhere that 16 dKH is the proper hardness for a reef
>tank. Is that correct?

You ask a question of religion.  There are as many "correct" values
as there are reefkeepers.  However, those who advocate such high
carbonate hardnesses as 16 dkH (seawater is around 7 or 8, for
comparison) are usually those who do not watch their calcium levels;
probably because such a high carbonate hardness can drastically lower
the calcium levels.  Trying to drive you tank so far out of
equilibrium is a never-ending chore.

After some experimentation I personally am maintaining around 10 dkH
or a bit above.  with this carbonate hardness and ~400 ppm Ca++ or
a little more, replacing the evaporated water with limewater
(kalkwasser, saturated Ca(OH)2 ) keeps things nearly constant.  Every
week or two I might have to bump up the calcium or carbonate hardness
by a little bit.

Dustin, who drove himself mad for a long time on this subject.

Calcium level

by kvk/ (Ken Koellner)
Date: 28 Jul 1993
Newsgroup: rec.aquaria

In article <> (Paul Ko          CSC) writes:
>Hi there!
>I just bought Lamott's Calcium test kit and the Alkalinity test kit. I just
>would like to know what is a good calcium level for a reef tank. (in units
>of ppm).

400ppm Ca+

You have to multiply your tritrator reading by the SW dilusion factor
(29.5?)  and then by .4 to get ppm Ca+.  I believe the instruction
explain that though.

>Also, how do you convert the Lamotts alkalinity test kits reading in ppm to
>dKH? I think I read somewhere that 16 dKH is the proper hardness for a reef
>tank. Is that correct?

	50 ppm = 1 meq/l = 2.8dKH

The recommended value is about 2.5-5.0 meq/l.  The important thing
is to keep it above 2.5.  I try to keep my tanks level around 3.0.
           Sig down for repairs.  Stay tuned for new, improved sig.          

Test Kit Information and Others

by ahughes/ (Arch Hughes)
Date: 5 Nov 92
Newsgroup: sci.aquaria,rec.aquaria,alt.aquaria

As per the request of Mr. Pineda, I am posting his study results.
Hopefully your follow-ups and replys will be directed to him because I
put Fernando's address in those fields (and because you'll be carefull
that you direct them his way)!

~From: Fernando Pineda <>
I noticed that my recent water chemistry post was corrupted. I'm not quite
sure what's happening. It appears that parts of my posts are being swallowed at
random by the network or by my system! Any advice from anyone with similar
strange experiences would be appreciated. I'm using TCP/Connect II under
multifinder on a Mac IIfx. In anycase, here are the notes including the calcium
buffering experiment, some simple calculations and the description the LaMotte
tesk kits.


My initial question about converting ppm CaCO3 to dKH resulted in an
explanation of the qualitative facts about hardness and alkalinity. My request
for the quantitative implications did not,however, meet with much success. So I
dusted off my old chemistry books, went to the library, did a few experiments,
and made some phone calls. The result of this little exercise is a set of notes
that may be useful to others who are trying to understand whatUs going on.

These notes are still incomplete, but if there is sufficient interest I will
continue to post my notes as I go along.


There are two main sections here. The first section summarizes the essential
quantitative facts needed to understand and visualize some aspects of water
chemistry. The second section gives detailed information about test kits, i.e.
what they actually measure and how they do it (chemistry!). This information
was obtained by calling around to the manufacturers and discussing the
chemistry of their kits. Also several people contributed via e-mail. I only
have experience with the LaMotte calcium kit so I may have missed some
information on the other kits.

LaMotte (and Hach) make test kits that measure total Calcium in solution and
test kits that measure both Calcium and total hardness. With the latter kits
you can estimate magnesium hardness too, but this is not too useful for
aquarists. For people that have Ca hardness test kits I describe a delightful
experiment that illustrates how the buffering effect of CaCO3 maintains the
level of free Ca++ ions in solution. It demonstrates that that the time scale
of the CaCO3 equilibrium reaction is ~5 seconds or less.

The terms RCarbonate HardnessS and RCarbonate AlkalinityS are identical. They
both refer to HCO3- and CO3-- concentrations. Measurements of these quantities
are only indirectly related to the amount of calcium in the water through the
reaction CaCO3 + CO2 + H2O <=> Ca++ + 2[ HCO3-].

Thiel refers exclusively to dKH in his book (Advanced Reef Keeping). He gives
18.9 as the conversion factor to go from dKH to ppm CaCO3. Two points here.
First, ThielUs carbonate hardness test kit actually measures total alkalinity
but the difference between total alkalinity and carbonate hardness  is only
about 3%, so for us aquarists, thereUs no point in making an issue of it.
Second, according to Thiel, you can convert from his dKH figures to total
alkalinity in ppm CaCO3 by multiplying the dKH figure by 18.9. I work through a
detailed example calculation below. Moe and Thiel donUt completely agree on
their ppm CaCO3 to dKH conversion factors. Moe gives the conversion factor as
17.9 or 1/0.05 = 20, Thiel says 18.9.  The difference may be related to the ~3%
difference between total and alkalinity and carbonate alkalinity, but without
further information I canUt determine this. In any case, neither Moe nor Thiel
gives a satisfactory explanation of the RgotchaUsS involved in these

Also, IUm still looking for more detailed data on the following test kits:
Hach, Tetra, others?. If folks would provide me with customer service telephone
numbers and as much information about a particular kit as they have, I can try
to follow through and get more detailed information on their kits. I might add
that, I donUt have infinite funds to spend on phone bills, so if anyone else
feels motivated to call and get information on a particular test kit, that
would help out considerably.


Concentrations are often stated as milligrams (mg) per liter (l) of fluid so
the units are (mg/l). One liter of water weighs almost exactly 1 kg = 1000
grams . So concentrations are often given in terms of (mg/kg). Now a milligram
is  1/1000000 of a kg or 1 part per million ( 1 ppm). So for our purposes,  we
have that...

                                1 mg/l = 1 mg/kg = 1 ppm.

Concentrations of a chemical species are often given in units of moles per
liter. A mole is 6.022x10^23 molecules (a very large number).

When you see square brackets around the symbol for a chemical species
(e.g. [HCl] ) it refers to the concentration of that species. Usually

one atom of Hydrogen weighs 1.6725x10^-21 mg (mg = milligrams)

Atomic and molecular weights are given in multiples of the weight of hydrogen

element         symbol  atomic weight
hydrogen        H        1
Carbon          C        12
Oxygen          O        16
Calcium         Ca       40

Molecules           composition(symbol)     molecular weight

Water               H2O                     18
Carbon Dioxide      CO2                     44
Carbonic Acid     H2CO3                   62
Calcium Carbonate   CaCO3                   100
Carbonate           CO3                     60
Bicarbonate         HCO3                    61

Example calculation -- How much does a mole of Bicarbonate weight?

>From the table we find that a bicarbonate molecule weighs 61 times as much as
a hydrogen atom. A mole of bicarbonate molecules is 6.022x10^23 molecules.
and one atom of Hydrogen weighs 1.6725x10^-21 mg, thus a mole of Bicarbonate

(6.022x10^23) x (61) x (1.6725x10^-21 mg) = 61,437 mg = 61.4 grams

Similarly, we can do a  mole of Calcium carbonate and discover that 1 mole
of CaCO3 weighs 100.7 grams.


Equivalent weight is a concept that comes up when dealing with acids.
One "equivalent weight" is the weight of a substance needed to provide ONE
mole of Hydrogen ions.


Each ion of Bicarbonate (HCO3-) can only contribute one Hydrogen ion. So
one mole of  Bicarbonate is "equivalent" to one mole of H+. As we saw above,
one mole of Bicarbonate weighs 61.4 grams. So, we say the weight of one
equivalent of Bicarbonate is 61.4 grams.

What about carbonic acid? Well carbonic acid (H2CO3) contributes two H+ ions
per molecule. So it only takes 1/2 mole of carbonic acid to make a mole of H+
ions. So one weight of one equivalent of Carbonic acid is...

(6.022x10^23) x (62) x (1.6725x10^-21 mg) = 62,445 mg = 62.4 grams

1 equivalent of  H2CO3 = 1/2 * (weight of 1 mole  H2CO3) = 31.2 grams

We will mostly deal with milli-equivalent weights (meq) which is 1/1000 of
an equivalent weight. So we have

1 meq of HCO3  = 62.4 mg
1 meq of H2CO3 = 31.2  mg

Finally, we are ultimately interested in concentrations which are usually
stated as milligrams (mg) per liter (l) of fluid so the units are (mg/l).

(1 meq of HCO3)/l  = 62.4 mg/l of HCO3 = 62.4 ppm
(1 meq of H2CO3)/l = 31.2  mg/l of H2CO3 = 31.2 ppm

This same idea of equivalent weights gets used when dealing with Carbonate
hardness. In that case the one "equivalent weight" is the weight of CaCO3
needed to provide ONE mole of HCO3- or CO3--.

The point about CaCO3 equivalent weights is that they are not physical
concentrations of CaCO3. Instead it is the amount of CaCO3 you WOULD get IF you
combined the physical amount of HCO3- and CO3-- with enough Ca++ to use up all
the HCO3- and CO3--.

The following is taken from RChemical Oceanography, Millerno & Sohn, (1992).

"The total alkalinity of seawater is defined as the concentration of all the
bases that can accept H+ when a titration is made with HCl to the carbonic acid
endpoint."  (p. 283)

note: I assume that the carbonic acid endpoint refers to the point at which all
the carbonate and bicarbonate bases in the solution have been bound with H+ to
form carbonic acid.


Total Alkalinity =  [HCO3-] + 2[CO3--] +        [B(OH)4-] + [SiO(OH)3-]
+ [MgOH+ ] + [ OH- ] + 2[ HPO4- ] + 3[PO4---]

Carbonate Alkalinity = [HCO3-] + 2[CO3--]

COMPOSITION  various bases contributing to total Alkalinity (at 25 degrees C?)
             in Seawater

                BASE       percent (by moles/liter )
                HCO3-     89.8
                CO3--        6.7
                B(OH)4-    2.9
                SiO(OH)3-  0.2
                MgOH+      0.1
                OH-        0.1
                HPO4-      0.1
                PO4         ?

note: As you can see from the table, the difference between carbonate
alkalinity and total alkalinity is only about 3%. This difference is probably
much less  than the precision of the test kits commonly available to aquarists.


Illustrative experiment and calculation # 1:
                Free Ca++, bound Ca (CaCO3) and equivalent CaCO3, CaCO3 bufferin

>From the atomic weight tables we see that 40% of the weight of CaCO3 is in Ca++

and the rest is in CO3--. Thus every 40 mg of Ca++ can form 100 mg of CaCO3.
That means that to get the CaCO3 equivalent of X mg of Ca++ you have to
multiply X by 2.5.

I bought a bottle of CaCO3 tablets and some distilled water (calcium carbonate
tablets available as Rcalcium supplementsS in the vitamin section of the local
drugstore, distilled water is usually available in the contact lens or water
section). The tablets I bought had 1500mg of CaCO3 each. I dissolved 1 tablet
in 0.1 liters of distilled water. I let my solution sit for a few days. Most of
the tablet wound up at the bottom of the beaker as a white powder.

I measured the Ca++ concentration using my LaMotte Ca test kit and got 64ppm
Ca++ (160ppm CaCO3 equivalent). So the 0.1 liter of water had 6.4 mg of Ca++ or
16 mg CaCO3 equivalent. This drives home the point that the CaCO3 equivalent is
not the same as CaCO3 actually added to the solution since I added 1500mg of

Now, lets see the buffering effect of CaCO3 directly! You may want to read the
writeup below on the LaMotte Ca test kit. The test kit measures Ca++ directly.
In the process of measuring the Ca++ it removes all free Ca++ from the solution
by binding it to an indicator (calcon). The calcon turns red when bound to
Ca++. Next an EDTA solution is titrated into the solution which in turn strips
the Ca++ from the Calcon. The Calcon turns blue when the EDTA has removed all
the Ca from it and the titration is over.  Now think about the following
equilibrium equation

                 CaCO3 + CO2 + H2O <=> Ca++ + 2[ HCO3- ].

In the process of performing the titration, we have unbalanced the equilibrium
since the Ca++ has been removed from the right hand side. Physics demands that
some of the 1500mg of CaCO3 disassociate to rebalance the equation. So after
five seconds or so, your blue indicator turns red again! (WOW!)

Effectively, the calcon acts like a Ca++ sponge that is red when it is RwetS
and blue when it is squeezed Rdry.S The RspongeS is wrung out when you titrate
the EDTA. Each time you sop up all the Ca++ from the solution, the CaCO3 buffer
simply replaces it. This replacement takes less than 5 seconds, so it takes
about 5 seconds for the RspongeS to turn red after you have RwrungS it out. Try
it: keep adding EDTA until the solution turns blue, then wait a few seconds
until it turns red again. Add more EDTA until it turns blue, then wait a few
seconds until it turns red again, add more...Once you get this going it only
takes one drop to perform a blue/red cycle.

Sea water and aquarium water probably has very little CaCO3 floating around.
Most of it is bound up in the rocks, corals and sediment. So it is unlikely
that youUll see this effect when you test your aquarium water unless you happen
to have stirred up some sediment.


Illustrative calculation #2: Alkalinity -- converting from meq/l to ppm to dKH

Note: This is in here so you can see how the alkalinity and hardness fits
together quantitatively.

Moe states on p.34 of his Marine Reference that Sea Water has an ALKALINITY of
2.1 to 2.5 meq/l. HeUs not specific, but probably he means TOTAL alkalinity of
the species given above. We can make a simplifying assumptions to make this
calculation easy. If we assume the measurement was taken at a pH=8.2 and at
T=24 degrees C, then about 90% of the alkalinity is in the form of HCO3- (see
e.g. the composition table above). This means we can expect at most a 10% error
in our calculation if we assume that all the alkalinity is in the form of HCO3-
. We know that each meq of HCO3 is 1/1000 of a mole of HCO3-. So there must be
2.1x10^-3 moles of HCO3- in solution. To calculate the CaCO3 RequivalentS to
this much HCO3- we calculate the weight of CaCO3 if all the HCO3- were to bind
with Ca++. The reaction is

            CaCO3 + CO2 + H2O <=> Ca++ + 2[ HCO3- ].

We see  that each mole of HCO3- will produce half a mole of CaCO3. So we will
be left  with 1.05x10^-3 moles of CaCO3. This will weigh

(1.05x10^-3 moles)x(100.7 grams) = 105.7 mg of equivalent CaCO3.

or 105.7 ppm equivalent CaCO3.

Finally,  letUs convert this to dKH. The significance of the conversion factor
is not clear to me. Furthermore Moe and Theil disagree on the exact conversion
factor. Moe (p.36) says it is either 17.9 or ~1/0.05 (p.36) while Thiel (p.101)
says is is 18.9 . Lets take 18.9. This produces 105.7 ppm CaCO3/18.9 = 5.6dKH
which is in the right ball park. Similarly 2.5 meq/l of HCO3 translates into
6.65 dKH. This is a reasonable answer for sea water.
Note that the actual physical weight of HCO3- in solution can be calculated
from the alkalinity of 2.1 meq/l according to (2.1 meq/l HCO3) x 61.4
ppm/(meq/l) = 128.9 ppm of HCO3-.



Advanced Reef Keeping 1, Albert J. Theil,Aardvark Press, Bridgeport CT,(1989)

The Marine Aquarium Reference, Martin A. Moe, Green Turtle Publications,
Plantation FL, (1989)

Chemical Oceanography, Frank J. Millero and Mary L. Sohn, CRC Press, Boca Raton
FL, (1992).

KIT:       The LaMotte Test kit (Model CA-DR, Code:3609)

MEASURES:  This test kit measures Ca++ directly.


The reading is given in units of ppm Ca++ or in ppm (CaCO3 equivalent).


Reagent #1:  Sodium Hydroxide.

This boosts pH to 12-13 so titration will work and also precipitates
out of solution the Magnesium as magnesium oxide. This leaves only Ca
in solution (and trace amounts of other metals).

Reagent #2: Calcon

This is an indicator with a strong affinity for calcium. It bonds
to all the Ca++ in the solution. All the calcium (free Ca++ or
CaCO3) in the sample is eventually bound to the indicator. The
indicator is red when bound to Ca and blue when not bound to Calcium.

Reagent #3: EDTA a chelating agent

The EDTA has an even higher affinity to Ca than the
indicator. So as the EDTA is added to the solution,
it strips the Ca from the indicator in proportion to the amount
of EDTA added. When no Ca remains bound to the indicator it turns
blue. The amount of EDTA added to the solution up to this
point is proportional to the amount of Ca that was in solution.


LaMotte technical assistance 1-800-344-3100
KIT:       The LaMotte Test kit (Model <>?, Code:4824)

MEASURES:  This test kit measures Ca and (Mg++, Fe++ etc.) or just Ca++


The reading is given in units of ppm Ca++ or in ppm CaCO3  equivalent.


With this test kit you can measure either Ca hardness or total
hardness. Also, since 99% of total hardness in sea water consists of Ca
and Mg, you can estimate Mg hardness by doing both tests and
subtracting the Ca hardness from the total hardness)

Besides the reagents found in the Ca hardness kit (code: 3609) this
kit contains an additional indicator Eriochrome Black T which binds
to all divalent ions.

The Calcium test has the same chemistry as described above in the
Ca Hardness test kit. The chemistry for the total hardness test kit is
as follows:

Reagent #1:  Sodium Hydroxide.

This boosts pH to 10. So titration will work.

Reagent #2: Eriochrome Black T

This is an indicator with a strong affinity for all divalent ions( Ca++,
Mg++, Fe++, etc.)  All the divalent elements are eventually bound to
the indicator. The indicator is <color>? when bound to divalent ions
and <color>? when not bound the divalent ions.

Reagent #3: EDTA a chelating agent

The EDTA has an even higher affinity for the divalent ions
than the indicator. So as the EDTA is added to the solution,
it strips the divalent ions from the indicator in proportion to the
amount of EDTA added. When no divalent remains bound to the indicator
it turns <color>?. The amount of EDTA added to the solution up
to this point is proportional to the total amount of divalent elements
that were originally in the solution.


LaMotte technical assistance 1-800-344-3100

KIT:       Thiel Aqua-tech (Model: Carbonate Hardness, KH Test, Product No:1111)


Customer service at Thiel claims that the test kit measures
Calcium Alkalinity [HCO3-, CO3--]. Their chemistry, however is a standard HCl
titration, therefore they are actually measuring TOTAL alkalinity. In any case,
at normal temperatures (25 C) this amounts to only a 3% error  (see ALKALINITY

UNITS: dKH  -- after applying a conversion factor that the kit supplies (2.8).


Instead of separate reagents the Thiel kit combines two reagents into a single
squeeze bottle.

Reagent #1:
A pH indicator dissolved in a dilute HCl solution (0.5% ?).
(Theil Aquatek would not reveal the particular reagent nor the exact dilution
of the HCl). The reagent is yellow-orange in the squeeze bottle. The indicator
is  yellow orange when in an acid and turns blue when the pH increases above
some value. I don't know the value but I guess that it is less than pH 6 or 7.

The HCl/indicator reagent is initially orange-yellow. When it is first added to
the sea-water solution it turns blue since the sea water is very basic compared
to the dilute HCl. As more reagent is added to the solution the HCl
disassociates into H+ and Cl-. The H+ binds with the bases until there are no
free bases left. At this point the H+ ions remain free, the solution becomes
acidic, and the pH drops dramatically. The indicator reverts to its yellow-
orange color. The amount of HCl added to the solution up to this point is
proportional to the total alkalinity.


Theil technical assistance 505-526-4000, (Al Bear)


The reagent bottle comes "unpierced".  You have to poke a pin
through it.  It looks like (though I have not measured it) it would
hold about 5 cc of the reagent.  On occasion, the bottle won't
"behave" well and an air bubble forms at the tip while I'm making
drops and it becomes harder to count "good" drops.  Once in a long
while, I'll see a little "spray" (a few very tiny drops) come out
while I'm forming a "real" drop and I have to make a call about whether
to count that spray as a drop or not.  (Each drop only represents a
0.7 dKH step (computed as 2.8/4), so it's not very critical when your
result is in the mid teens.)

It (the test kit) comes with a nice 15 cc translucent plastic test
vial with red imprinted graduations, the single sheet instructions,
and all in a "zip lock" plastic bag.
My impression is that it doesn't provide anything close to the 50 tests
that the TFP catalog lists it as providing.  I'd say it provides more
like 10 or 15 tests.  Of course, mileage varies depending on your
KH....the higher the KH, the more reagent you use per test, and the
fewer tests you'll end up making per purchase.

"That Fish Place" item 055056, $12.95 each ($10.95 on sale now)
KIT:       Hach (Model ?, Code:?)

MEASURES:  Ca and total Hardness

UNITS:     ppm CaCO3, ppm Ca++




It gives results as mg/l of CaCO3.  I only use the calcium part of the kit as
that's what I care about.  I did measure the total hardness of my tap
water when I first got it just to see what it was.  Total hardness is
meaningless to saltwater keepers.


Hach technical assistance telephone number
KIT:       Tetra (Model ?, Code:?)






Hach technical assistance ?



by cb77/ (Craig Bingman)
Date: 14 Feb 1994
Newsgroup: alt.aquaria,rec.aquaria,sci.aquaria

In article <2j95r6$>,
JEFF PFOHL <> wrote:
>Is it possible, from the point of view of the health of the
>inhabitants, to add too much calcium to a reef tank? 


>I wonder since
>the inhabitants need a constant supply, and it helps grow good algae
>while preventing bad algae that it  might be best to err on the side
>of excess rather than have too little. 


>Also, does anyone
>know if Theil makes a calcium supplement that is NOT kalkwasser? I
>cannot seem to find it anywhere!

Who cares?

OK, now for a serious answer to your question.  

There is a "yin/yang" relationship between calcium concentration and
carbonate ion concentration.  The relationship is encapsulated in the
following equation.

Ca++(aq)  + CO3--(aq)  <--->  CaCO3(solid)

Obviously, increasing the calcium concentration indefinitely will
eventually result in precipitation of CaCO3 (at typical alkalinites/
pH/carbonate concentrations.)

There are a number of implications of inorganic calcium carbonate ppt.
Among them:

1.  you lose both dissolved calcium and alkalinity (buffering capacity)
2.  you may clog your pumps
3.  you may upset the hell out of everything in the tank when CaCO3
    falls on it like snow.
4.  there may be pH fluctuations during the event.  (although I think
    that I am the only one who has seen this effect, and that was in
    the lab when I really pushed the Ca++ concentration to astronomical
    levels.  The HCO3- concetration was way up there, too.)
5.  you will be frustrated as hell if you are always trying to hit
    a calcium/alkalinity target that is too high.

Marine water is fairly close to "saturation" with respect to CaCO3.
Simplistic calculations indicate that it is supersaturated.  More
realistic calculations, including ion-pairing effects (primarily
Mg++ / CO3--) indicate that it is slightly under saturation, under
usual temperatures and salanities.  Inorganic precipitation of CaCO3
is a fairly rare event, but does occasionally happen in hot, shallow,
saline water.

I've written quite a lot on this topic, some of it was posted to the
net, and some of that is apparently in Dustin's archive.  There are some
trivial but almost totally neglected relationships between calcium 
concentration and alkalinity (HCO3-/CO3-- concentrations in particular)
that are described in excrutiating detail in those notes.  I've also
written about the implications of various calcium additives (Ca(OH)2 and
CaCl2 in particular) on the long term stability of the water chemistry
in the tank.

I should really write this up and send it off somewhere so I can just
tell people to go read it.

About Thiel.  He apparently sells a calcium additive called "pure
calcium."  I don't know what is in it.  He won't say.  It most
assuredly is not "pure calcium" though, since that would be solid,
metallic Ca.  More marketing hyperbole from the master of marketing 
BS himself.

I would not recommend that anyone put an unknown chemical in their tanks.

Read the archived articles on calcium.  Try using kalkwasser.  If it
doesn't work, try it again.  ;-)  As a last resort, use CaCl2, then
try kalkwasser again.

Best of luck,

Up to Marine/Reefs <- The Krib
This page was last updated 29 October 1998