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CO2 Test kits

Contents:

  1. CO2 test kit recommendations
    by George Booth <booth-at-hpmtlgb1.lvld.hp.com> (Wed, 13 Sep 1995)
  2. CO2 determination and Tannin/Humic Acid levels
    by "James Purchase" <jpp-at-inforamp.net> (Fri, 17 Jan 1997)
  3. ph Testing
    by Daniel Marsh <dmarsh-at-premier1.net> (Thu, 16 Jan 1997)
  4. CO2 tests
    by George Booth <booth/hpmtlgb1.lvld.hp.com> (Mon, 20 Oct 1997)
  5. Ca and Mg Measurements
    by Augustine Rodriguez <rodrigaj/win.bright.net> (Tue, 16 Jun 1998)
  6. "Absolutely essential" test kits (M)
    by patti/hosehead.intel.com (Patti Beadles) (Mon, 27 Jan 1992)
  7. (No Title)
    by ()
  8. For the archive, discussion of seachem alkalinity test
    by Craig Bingman <cb77/columbia.edu> (Fri, 16 Dec 1994)
  9. [R] Ca(OH)2 additions
    by cb77/aloha.cc.columbia.edu (Craig Bingman) (17 Dec 1994)

CO2 test kit recommendations

by George Booth <booth-at-hpmtlgb1.lvld.hp.com>
Date: Wed, 13 Sep 1995

Here's some info from the Hach Water Testing Handbook (free for the
asking): 

  Hach Company
  PO Box 608
  Loveland, CO
  80539-0608

  phone (800) 227-4224
  in Colorado (303) 669-3050


CARBON DIOXIDE TEST FOR WATER AND SEAWATER

Introduction
- ------------

Carbon dioxide is present in all surface waters, generally in amounts
less than 10 mg/L.  However, higher concentrations are not uncommon in
ground waters.  Dissolved carbon dioxide has no harmful physiological
effects on humans and is used to recarbonate water during the final
stages of water softening processes and to carbonate soft drinks.
High concentrations of carbon dioxide are corrosive and have been
known to kill fish.

The anlysis for carbon dioxide is similar to that for acidity.  A
water sample is titrated to a phenophthalein end point with Sodium
Hydroxide Standard Solution. Strong mineral acids are assumed to be
absent or to be negligible in effect.  Care must be taken during the
anlysis to minimize the loss of carbon dioxide from the water sample
as a result of aeration when collecting and swirling the sample.

Chemical Reactions
- ------------------

The reaction of sodium hydroxide with carbon dioxide (as carbonic
acid) occurs essentially in two steps, first a reaction from carbonic
acid to bicarbonate and then to carbonate:

  CO2 + H2O -> H2CO3

  H2CO3 + NaOH -> NaHCO3 + H2O

  NaHCO3 + NaOH -> Na2CO3 + H2O

Because the conversion of carbon dioxide to bicarbonate is complete at
pH 8.3, phenophthalein can be used as a color indicator for the
titration.  The sodium hydroxide titrant must be of high quality and
free from sodium carbonate.


CO2 determination and Tannin/Humic Acid levels

by "James Purchase" <jpp-at-inforamp.net>
Date: Fri, 17 Jan 1997

Hi Everyone,

Thanks to Paul and Dave for their clarifications on Alkalinity. I agree
about the weakness of most aquarium trade books on the subject of water
chemistry. Its a good thing that most plants and fish are so adaptable and
can live in a wide range of conditions. But this list is read by people who
wish to optimize their aquarium's ability to maintain aquatic plants and we
should have better resource material. Maybe I'll write a FAQ once I get a
really good handle on this. I'm glad I never got rid of my university
chemistry texts.

I have noticed a number of posts on the reliability of CO2 test kits and
how their results may vary from published tables, such as the one in The
Optimum Aquarium and the one that George Booth recently posted. I contacted
LaMotte and asked them about the discrepancies and also about interferance
from tannins and humic acids in the water of many aquariums. The answer
might surprise some people:

_______ E-Mail from LaMotte Technical Services ______________________

The test method for carbon dioxide is an acid/base titration: meaning that
a
base (sodium hydroxide) is added to the sample until it neutralizes all of
the acid in the sample and brings the pH of the sample up to 8.3 (shown by
the color change of phenolphthalein).  Carbon dioxide in water is an acid,
so
it is titrated by the base.  But, any other acid in the sample will also be
titrated by the base, including the humic acid in your sample.  Also, any
bases already in the sample will affect the titration.  Unfortunately,
there
is no way to accurately calculate out these interferences.

For this reason the carbon dioxide titration test is considered to be a
quick
field test method, only.

The nomographic method is more accurate, if the pH and alkalinity are
measured accurately.

I am not sure what levels of tannin are in you water.  So I am not positive
that our tannin test kit will work for you or not; it does not read below
1ppm.  But, it is possible that you have levels higher than that, due to
the
nature of your set up.  If so, the kit should be just fine.  Most of our
distributors do no stock the tannin kit, since it is not widely used.  You
can, however, buy it directly from LaMotte for $54.35.  You can do this by
calling 800-344-3100, asking for Customer Service, and requesting a 7831
tannin kit.
____________________________________________________________

So it would seem from this that when trying to determine the CO2
concentration of our tanks, it would be better to rely on accurate
measurement of pH and Alkalinity, and use the CO2 test kits as a fall back
only. Wish I had known this before I laid out the money for the Lamotte CO2
Test Kit (we all live and learn I guess). Does anyone know how accurate
those battery operated pH "pens" are?
...

James Purchase
Toronto, Ontario 


ph Testing

by Daniel Marsh <dmarsh-at-premier1.net>
Date: Thu, 16 Jan 1997

Augustine wrote:

> When using the Hach CO2 test kit, care should be taken when removing the
> water from the tank.  When you remove the water try not to pour it into the
> test bottle.  I have used a plastic measurement syringe successfully for
> this purpose.  You are measuring carbonic acid.  Your end point is the
> first point at which the solution turns a light pink.  I use a reference
> solution of DI water in a second test bottle.  I place both bottles on a
> white surface, side by side.  The endpoint is obvious when you compare the
> two bottles - even though it is light in color.

Your suggestions for reading the CO2 test were very helpful, especially
using the reference solution, it is _very_ light pink but I can see it.

We sent to Hach for their 7.0 buffer to test the phenol red reagent
against, as per their instructions, and found it to read 7.0 perfectly.
However we found that our ph meter read the new buffer -at- 7.2 ,which
sheds some light on the problems we've been having :-).

Our test results are now starting to make sense. 

Thank you very much for all your suggestions and help, they are greatly
appreciated.

Rebecca and Daniel Marsh
In currently stormy Gold Bar, Washington where the tap water content
changes almost as fast as the weather

CO2 tests

by George Booth <booth/hpmtlgb1.lvld.hp.com>
Date: Mon, 20 Oct 1997

> Date: Sat, 18 Oct 1997 14:03:37 -0400
> From: Ed Hengel <hengel-at-computer.net>
> 
> > I'm unfamiliar with the LaMotte Test Kit but....
> > 
> > If the CO2 reading is obtained by titrating the water sample with
> > Na2CO3, then free mineral acid, if present, will be measured. Also,
> > heavy metals such as iron, chromium, and aluminum salts interfere.
> > This from the Betz Handbook of Industrial Water Conditioning.
> 
> Does anyone know if this is the case with the LaMotte kit?

>From the LaMotte Water Test Handbook (free for asking, I think):

=======================
CARBON DIOXIDE FOR WATER AND SEAWATER

Introduction
- ------------

Carbon dioxide is present in all surface waters, generally in amounts less
than 10 mg/L.  However, higher concentrations are not uncommon in ground
waters.  Dissolved carbon dioxide has no harmful physiological effects on
humans and is used to recarbonate water during the final stages of water
softening processes and to carbonate soft drinks.  High concentrations of
carbon dioxide are corrosive and have been known to kill fish.  

The analysis for carbon dioxide is similar to that for acidity.  A water
sample is titrated to a phenophthalein end point with Sodium Hydroxide 
Standard Solution. Strong mineral acids are assumed to be absent or to be
negligible in effect.  Care must be taken during the anlysis to minimize the
loss of carbon dioxide from the water sample as a result of aeration when
collecting and swirling the sample. 

Chemical Reactions
- ------------------

The reaction of sodium hydroxide with carbon dioxide (as carbonic acid) occurs
essentially in two steps, first a reaction from carbonic acid to bicarbonate
and then to carbonate:

  CO2 + H2O -> H2CO3

  H2CO3 + NaOH -> NaHCO3 + H2O

  NaHCO3 + NaOH -> Na2CO3 + H2O

Because the conversion of carbon dioxide to bicarbonate is complete at pH 8.3,
phenophthalein can be used as a color indicator for the titration.  The sodium
hydroxide titrant must be of high quality and free from sodium carbonate.
=======================

George
 

Ca and Mg Measurements

by Augustine Rodriguez <rodrigaj/win.bright.net>
Date: Tue, 16 Jun 1998

Michael Schmidt wrote:

>It will tell you the sum of Ca and Mg. But plants have different
>requirements for the two, and it would be best to know each separately.

The Hach Total Calcium and Magnesium Hardness Test Kit does that. Model
HA-4P, Cat. No. 1457-00.

First, you get a Total Hardness reading with one sample. Then using another
sample, you measure for Calcium Hardness. To obtain the magnesium hardness,
you subtract the calcium hardness value from the total hardness value.

Iron will interfere with the results of this test in concentrations above
8ppm, Manganese above 5ppm. Other warnings are given for Al, Ba, and Sr,
but should these should not be found in typical aquarium waters to
significantly affect readings. High orthophosphates can cause slow end
point titration times.

I've used this test kit for three years because I have very soft well
water, and must supplement my aquarium water with Ca++ and Mg++. I have
tested the results against lab standard solutions, and the results have
always been accurate and repeatable.

I would highly recommend this test kit to anyone looking for a good
(albeit, expensive) kit.

Augustine Rodriguez
Elk Mound, WI, USA


"Absolutely essential" test kits (M)

by patti/hosehead.intel.com (Patti Beadles)
Date: Mon, 27 Jan 1992
Newsgroup: rec.aquaria

In article <19415-at-attain.Teradyne.COM> brian-at-attain.icd.teradyne.com (Brian Hunter) writes:
>>In article <1992Jan22.170324.26972-at-ichips.intel.com> daveo-at-omews18.intel.com (David O'Brien) writes:
>>> Get the HACH Calcium test kit, *not* the Lamottes.  
>Several posts have mentioned this, could any one comment on why?
>More accurate or more easy to use?


(No Title)

by

>What is the Model number of the prefered HACH test kit?

The part number is 1457-01.
-- 
patti-at-hosehead.hf.intel.com |  I don't speak for Intel, nor vice-versa.
   75555.767-at-compuserve.com |
             (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.


For the archive, discussion of seachem alkalinity test

by Craig Bingman <cb77/columbia.edu>
Date: Fri, 16 Dec 1994
To: "Dustin L. Laurence" <laurence/Alice.Wonderland.Caltech.EDU>

Dustin,

Could you please add this to the archive?  Thank you.

--------------------------------------
>From cb77-at-aloha.cc.columbia.edu Fri Dec 16 21:07:13 EST 1994
Article: 50619 of rec.aquaria

[R] Ca(OH)2 additions

by cb77/aloha.cc.columbia.edu (Craig Bingman)
Date: 17 Dec 1994
Newsgroup: rec.aquaria,sci.aquaria

In article <3ci2im$b8g-at-cuboulder.colorado.edu>,
DAVIS PATRICK W <davisp-at-spot.Colorado.EDU> wrote:
>In article <3cg5n9$k0-at-apakabar.cc.columbia.edu>,
>>Craig Bingman <cb77-at-sawasdee.cc.columbia.edu> wrote:
>>In article <3ca21u$747-at-cuboulder.colorado.edu>,
>>>DAVIS PATRICK W <davisp-at-spot.Colorado.EDU> wrote:
>>
>>It is sort of bizzare that your calcium level would drop that much without
>>the alkalinity coming down at the same time?  I would hazard a guess that
>>you are a fairly regular buffer adder, yes?
>
>The tank is about 1.5 months old. Using the SeaChem kit, I was measuring 
>about 1meq/l alkalinity (using Reef Crystals). Thinking the test kit MUST 
>be correct, I added SeaChem Marine Buffer to bring it up. It took about 2 
>weeks following their instructions. I'm hoping that the LaMotte kit I 
>ordered will give me an accurate reading.

OK, thanks for providing an opportunity for me comment on the Seachem
alkalinity test.  It is Very non-standard, and I am Very bothered by
the fact that the mfrg does not explain to customers not only are they
getting an alkalinity test, they are getting one with extremely non-
standard end-points.

My problems with this test are manifold.  Endpoints first.
The seachem test gives two kinds of alkalinity, and they appropriate
labels from standard water testing and give them non-standard meanings.
Carbonate alkalinity is usually measured to the phenolpthaleine endpoint,
pH=8.3.  The seachem test endpoint is in the 8.2-8.0 range, it is 
unclear to me what color they are talking about on the chart, and
I trust it will also be unclear to people who don't happen to have
doctoral degree in Biochemistry.

The endpoint for the total alkalinity test is 7.6.  This is total rubbish.
The proper endpoint for a total alkalinity determination is well below
pH 6, at the carbonic acid endpoint.  The actual pH chosen as an endpoint
is to depend on the total alkalinity in the sample, but it is around
2 pH units below the bottom of the seachem test.

So the test systematically underestimates alkalinity as compared to
standard tests.  I leave it to the reader's imagination the excercise
of figuring out why a complany that markets a line of buffers for
marine use would do that.

If you want to check the test yourself, mix up a fresh batch of
synthetic seawater, full strength.  Measure the alkalinity.  All the ones
that I have checked are 3.0+/- 0.5 meq/L.  Compare that to the value you
get from the seachem test.

I have some other problems with the test, the color chart is horrible,
the claimed sensitivity of this test to the pH range encountered in
marine systems is poor.  The resolution is the poor.  1 meq/L is just
not good enough for me when I am trying to measure an alkalinity that 
typically falls in the 3.0+/-0.5 range.

The seachem philosophy is to jack up the buffer concentration to the 4-6
meq/L range, and to use calcium chloride as the main calcium additive.
(I tried to get an answer out of Morin as to what happens when you try
to use the gluconate calcium product as the sole calcium additive, he
was evasive as typifies his responses to Anyone who knows what they are
talking about.  I assume that it won't work for one reason or another,
have a strong suspicion as to what happens, but it isn't properly
validated, so I'll reserve comment on that for now.)

So you are going to go through a Lot of buffer and calcium chloride if
your alkalinity is jacked up to 6 meq/L, the pH is 8.3, and the calcium
concentration is anything close to values typical of reef or open ocean.

Possible questions you might be asking yourself:  

Q:  There is a standard solution of Tris buffer included in the test.  How
could I be underestimating alkalinity if my results square with the 
expected results from the standard test?  

A:  The pKa for Tris buffer is 8.08.  The lower end of the alkalinity
    test is 7.6, half a pH unit below the pKa.  There will be little
    error in an alkalinity determination on Tris by this method.
    (for all I know, the Tris buffer supplied is standardized to
    give exactly 3.0 with the 7.6 endpoint.)  The pKa for carbonic
    acid is 6.35, well below the 7.6 endpoint of this alkalinity
    determination.  You can easily appreciate when most of the buffering
    capacity is below the lower end of the test, you are going to 
    miss it.

Q:  Why are they doing this?

A:  I have no idea.  Morin has a "thing" about controlling pH in aquaria.
    A great many of us have thriving aquaria with alkalinity in the 3.0
    to 3.5 meq/L range, AS MEASURED BY STANDARD TESTS.  

Q:  Isn't it a good idea to have a lot of buffering capacity in the
    aquarium?

A:  It is a good idea to have sufficient buffering capacity to prevent
    harmful pH excursions.  A great many of us find that the alkalinity
    values given above (3.0 to 3.5 meq/L as measured by standard tests
    are adequate for this purpose.)  Alkalinity values higher than that
    are not consistent with calcium concentrations near seawater levels.
    The ocean runs at about 2.5 meq/L alkalinity, pH around 8.3, with 
    calcium in the 10-11 mM range (400-440 ppm.)  It is also essentially
    saturated with respect to calcium carbonate (this is a topic in and
    of itself.)  If you want to double the buffer concentration to 
    5 meq/L, and if you do it with the same buffer substances at the same
    proportions as found in seawater, you are going to struggle to keep
    your calcium concentration above 250-300 ppm.

You didn't just buy a alkalinity test, you bought into a separate school 
of thought on how aquaria should be maintained, how calcium, alkalinity
and pH should be maintained.  You bought a very non-standard test, and
as far as I am concerned, the Minimal courtesy that Seachem could extend
to its customers is to tell them that their method is just that, non-
standard and will not agree with, for example, results from a Hach 
alkalinity test.

So, if you don't believe me, go look at some water analysis handbooks.

>>If so, what kind of buffer have you been adding, how often, etc? 
>>Where is the pH value for your system at lights on and lights off?
>>
>
>Using the SeaChem pH test, I can't even get +-.2, so I have no idea what 
>my pH is. Using the Kordon kit, I at least know I am in the right range. 
>I am getting a pH meter and probe together.

Yes, I have a very difficult time reading the pH test as well.

>>>(I was adding it b/c according to the Hach kit I just received my Ca is 
>>>about 200ppm. I guess that is why my coralline algae has stopped growing).
>>
>>Yes, that would pretty much do it.  ;)
>
>Actually, I misread the Hach kit instructions. My CaCO3 was 200ppm, my Ca 
>was 50ppm :( Now I know why I was getting a little bit of red algae to 
>form (with 0 phophates).

If your CaCO3 is 200 ppm, your calcium is 80 ppm.

You have added enough buffer to drive nearly all the calcium out of your
water.

You have a big problem.

I'm not going to tell you what to do with the Seachem test, but I encourage
you to buy a standard one.  Hach makes one that just isn't that expensive
when you compare it to what you get to do next.

You need to do a Lot of water changes on your aquarium.  The calcium/
alkalinity/pH are Hosed right now.  Try a 25% water change first, see
how things do, and if they are stable, go for a second 25% water change
the next day, and stay at that for at least four days.  During this period 
of time, I wouldn't mess with adding any calcium or alkalinity supplements.
By then, your Hach kit should have arrived, and you can figure out what
kind of alkalinity you really have.  Oh, please also do this.  Take a 
sample of your water, and put it aside.  A gallon or so.  Read it with
the standard alkalinity test kit when it comes in, and tell me what it
says.  I'd also love to do a borate test on your aquarium water, so if
it isn't that big a deal, hang onto a gallon of it, and I'll get back
to you with details on my plans for it.

Keep doing the water changes until you have a good kit.  Then you can
adjust the calcium and alkalinity of what is left.

I'll be out of town the 22nd-29th.  E-mail me if you have questions, 
so that I will be sure to see them.

Best of luck, and start those water changes.

Craig



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