Salifert use to or still does make a organic test kit . You can test GAC to see if it is exhausted using Methylene Blue. You can't test CO? with a kit but could buy a pCO? probe/meter. It is easier to just use our calculator for CO?.
Thanks! I was thinking about this because I know testing PO4 in and output of a reactor I can tell when GFO is exhausted because the number is the same,,,I was assuming when you add Activated Carbon maybe the system "knows" and I'd be able to test for it.
SIDE NOTE<<<EXCELLENT LINK!! Thanks!! Is there an optimum CO2 level for mixed reef w/fish?
On the GAC when you think it is time to change it run a diluted solution of MB. If the GAC is still removing the dye the GAC is not exhauste. However, you should try a fresh GAC sample and measure its time on how long it takes fresh GAC to remove the dye from the sample water. Don't look for the dye to be 100 % removed.
CO?, not really, there are to many variables but try to stay ~ 0.4 - 1.5 ppm. NSW is ~ 0.4 ppm. In aquariums 99 % of the time it is CO? that controls pH, not Alk. I don't care if your Alk is 20 dKh, if CO? enters the water the pH will drop period. And the lower the pH the higher the CO? and the higher the Alk the higher the CO?.