I would not recommend this kit to aquarium keepers. You are better off estimating CO2 levels using the KH and pH charts. The Lamotte CO2 kit, which I own and have used to test natural waters for research, may be inexpensive, but requires titration and most people will be put off by that. It's not that hard, but it is definitely more trouble than it's worth for home use. Roxanne Bittman