I am sorta new to SW Tanks and have an up and coming 125g Zoa and Poly tank. I have noticed in most of the larger tanks that I have seen on line they have these CO 2 containers. What are these tanks for and how are they used. My goal is to move up to at least a 200g tank at some point, are there any on line sources for info on setting up larger tanks. My tank is a ( sp: Berlin system) simple set up and I know my knowledge is going to have to increase alot before I go to a bigger tank. Thanks for your time.

