Re: [APD] Estimative Index for CO2 Dosing - Bah!

[gbooth at frii_com]

A few notes.

Yes, the "better" test kits are also affected by water chemistry.

The LaMotte alkalinity test kit measures alkalinity just like lesser test
kits.  It doesn't claim to measure KH.  If you have stuff in the water
that is seen as alkalinity, the results don't return a "KH" value. But the
value returned for alkalinity is more accurate (if you care at all).

The LaMotte CO2 test kit is used to titrate a water sample to a specific
pH for a color change. If you have stuff in the water that affects pH,
your results will be off by some amount. The instructions warn against
"strong mineral acids" which I suppose could include phosphate.

We had great success measuring pH, "KH" and CO2 and getting results
consistent with published CO2 tables and consistent with the error ranges
for the test kits.  At the time we were doing this, we were not adding any
phosphate what so ever.

Someone mentioned CO2 equilibrium values.  This was beat to death back in
the 90s and the theoretical value for CO2 equilibrium was 0.485 PPM (at a
specific temperature, etc).  However wonderful that theoretical number is,
the practical value is around 2-3 PPM.  Resolution was never reached on
why there was a difference but it was probably due to either
A) biological respiration (bacteria, algae, plants, fish) keeping ahead of
diffusion to the atmosphere,
2) the contrarian nature of aquarium water.

George B
Ft. Collins, CO


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