Amit, The water that was taken out of the tank was saturated with CO2. When the new water was added, you basically dilluted your CO2 saturated water so that the concentration of CO2 was less. Now your water has the ability to accept more CO2 untill it is saturated again. This is a normal occurance during a water change. If you lower your KH and the PH stays the same your CO2 levels are going to drop. I do not know if CO2 dissolves better in water with a low GH but what seems to be important to CO2 is PH and KH. ------------------ To unsubscribe from this list, please send mail to majordomo@thekrib.com with "Unsubscribe aga-member" in the body of the message. Archives of this list can be found at http://lists.thekrib.com/aga-member/