It is never an accurate way to measure CO2, but it will be as accurate as it always is. The key is that nothing in the water changes when it degasses except the amount of CO2 dissolved in it. The problem is that we never can be sure just how far outgassed it is, and the pH change depends on how far it outgasses.Bill said:So would measuring your pH and leaving it out and measuring it again in 24 hrs be an accurate way to measure CO2 with AS?
Tom Barr said:But.............
A sample of DI water (anyone can get some drinking water DI water at a store pretty easily) + baking soda will degas and hold the SAME CO2 content at the same time as the tank's AS sample..........
Both samples should have the same CO2 content since the partial pressure of CO2 is also the same................at least after say 1-2 days.
So if you wanted to do this to get the CO2 ppm in a peat water, ADA AS water, you can.
One measurement issue with the timing of the sampled CO2 can be overcome by a simple CO2 reference using pure water and the bicarbonate (KH) buffer to determine the CO2ppm and then assume this partial pressure of CO2 to be equivalent after say 48 hours or both samples under strong aeration for several minutes to degas.
It is possible and should be as effective as the pH/KH table is.
Could top off with more RO/DI if its very important to you. In the end such a skewing of the data is probably less than the %error of the test, so you can ignore it. Better guess is the most realistic goal with any hobby grade kit.My only reservation about trying to use this method is evaporation of the samples as they sit there outgassing.
VaughnH said:I agree, but it would be much more accurate than the ph/KH tables, since it would not require assumptions about sources of alkalinity or acidity. My only reservation about trying to use this method is evaporation of the samples as they sit there outgassing. Evaporation raises the KH. That kills the equation that relates pH drop to ppm of CO2. But, I don't have my head working well enough to see if the evaporation of both the reference sample and the tank sample, assuming both are in the same size and shape vessel, raising both of their KH's would compensate. Maybe when my brain is ready to shift into high gear again I will try to figure that out - but I hope someone with a finely tuned brain will beat me to it.
VaughnH said:In my condo 48 hours sitting on the kitchen counter in a wide mouth container would result in evaporation of about half of the water, and that would double the KH. You can add more DI/RO water to make up the difference, but that water would have to have been degassing alongside the other samples. Now, how do you make up the water loss in the tank sample? Would adding DI/RO water from an outgassed supply do it? Yes, tentatively, it looks like it would.
I threw up my hands when contemplating how long such a test would take, and all of the new errors that might be introduced. My last try was blowing into a sample of RO water to see if a repeatable amount of CO2 could be introduced without causing me to faint first. That's when I gave up totally on measuring CO2.