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Re: Lamotte CO2 test

James Purchase pointed out that:
> While you are checking out LaMotte kits, look for one of their narrow
> range
> pH kits. They aren't expensive and you'll get more accurate pH
> reading using
> a real pH kit than relying on a chart. There are several variables
> involved
> in using the chart - how accurate your 2 readings (CO2 and Carbonate
> Hardness) are and the CO2 test kit can be thrown off by old reagents
> quite
> easily (or by sloppy technique).
> 
> This isn't a place to cut corners. Buy the kits.

If you look at small differences in pH on the CO2-KH chart, you can see
that there is lots of room for 'error' working in either direction,
from pH to CO2 or vice versa.

The number of measurements increases the indeterminancy (or
underdeterminancy) of the final calculated result -- the elements used
in the calculation don't fully determine the true result because each
step introduces a little more margin of error.  Generally, single
indeterminacy is better than double.  

But I found some tests easier to read accurately than others and
imagine others might have the same experience.

Before getting a pH monitor, I used to have two other members of my
family confirm my pH test readings.  It was hard to get three people to
agree on a single reading.  We could usually get two but it's hard to
rule out peer pressure effects ;-) .  We last used Aquarium
Pharmaceuticals's pH test.  But we have the same problem with, for
examples, SeaChem's phosphate and nitrate tests.  So, I just hate them
darned color comparator tests.   

Worst conditions are when the comparator card is made in different
color tones than the test actually produces -- for example, the
comparator goes from yellow to red but the sample is pink.

BTW, after carefully calibrating the pH monitor, we found that all
three of us were wrong in our perceptions of the pH tests.  Generally,
we were not far off, but in terms of the CO2 chart, a little off in pH
can mean a big difference in calculated CO2 levels.

Also BTW, we all pass the tests that detect the types of color
"blindness" -- i.e., we aren't color blind, at least not in other
situations.

FYI, my 8 (tomorrow 9) year old daughter usually made the most accurate
reading of the pH test- generally being off only by about minus 0.2
(which can equate to a difference of over 100% in determining CO2
levels).

Since CO2 measurement tests actually test for acidity ( I think I said
that right) I doubt the accuracy gets any better going from CO2 test to
pH calculation.

Hint:  with the Aquarium Pharm. pH test, hold the vial right up against
the paper -- that might help you to get more accurate readings.

Can someone who finds the cheaper test kits hard to read accurately
attest to the expensive comparator kits (LaMotte or Hach) being
significantly easier to read accurately?

If you are considering what a high level Lights and a CO2 system cost,
consider also a pH monitor.

Neil Frank said that the System I was the best piece of equipment he
ever bought (or something roughly like that).  Right now, for my own
situation, my vote goes to my pH monitor.

Scott H.

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