CO2
 

Hey all, first time posting, awsome site.
What is CO2 used for in aquariums?

Welcome to the board!! CO2 use depends on what type of aquarium. In reef, it's used to feed a Calcium reactor, in which it lowers the pH of the water in an enclosed reaction chamber and this dissolves a calcerous media. This then maintains Ca and alk levels in the tank.

In freshwater tanks, its used to lower high pH... and in the case of FW planted tanks, its used to provide an abundant source of carbon for plants.

-Richer