01-10-2012, 12:17 AM
Join Date: Jan 2012
| | Re: API KH test kit - Anyone with experience? Measuring CO2 Amounts
Originally Posted by HeyPK
With my CO2 kit you titrate a sample of aquarium water with a NaOH solution until the indicator turns pink. You convert the # of drops into ppm CO2 using a chart. If you do 2 samples, one straight out of the tank and the other from the tank but allowed to stand for a day, and subtract, you get a more meaningful CO2 value. The CO2 that remains in water in equilibrium with the atmosphere isn't very much and isn't very available except for those plants highly adapted to being submerged and able to get CO2 from the bicarbonate ion, HCO3-, like Najas, Elodea, Ceratophyllum, etc.
That sounds terribly inaccurate. All you're doing is an acid/base titration so if there are any other things in the water acidifying it they will skew your results upward. Which is highly likely considering a lot of the biological processes involved in an aquarium will acidify your water by producing fulvic and humic acid, and then theres tannins if you have any driftwood. Measuring the pH difference is all you need. Which is pretty much what your describing in a roundabout way.
To the Big_Fish, atmospheric CO2 generally dissolves at 2.5-3ppm(pretty much exactly 1/100 of what is present in your ambient air and using 30ppm as 1 degree is a reasonable assumption). CO2 affects pH and if you isolate what is changing the pH to CO2 you get a measurement of CO2 as a factor of multiplication. CO2 is likely the only gas that changes pH in an aquarium, so by allowing the aquarium water to reach ambient levels of CO2 you will likely isolate CO2 as the culprit in any pH changes. pH is a logarithmic scale, meaning 1 degree=10 times the previous degree. So if you have a 1 degree drop you have 10 times what is present under ambient situations, and if you have less than 1 degree you can use the decimal as a multiplier against the total to get a rough idea of where your co2 is(e.g. if you have a .5 degree change you halve 30ppm to determine you have around 15ppm CO2.)