Co2 has drawbacks and benefits. Depending on your water source, and water specs in your tank. Co2 can help one achieve a stable acidic PH with an automated system, but can kill everything in a system that you test manually. In an alkaline enviro, they can be used to break down calcium to raise PH and alkalinity. On a full set up with auto control, look to spend about $400. Can be cheaper depending on the situation.
