Ok. I'm a bit confused on how to set up CO2 and what I need to buy. I'm setting up a 40 gallon and want to use CO2 and may even consider it on my 10 gallon if my plants struggle. I tried to read through the stickies but got a bit lost. Advice and an explanation of what I need would be so helpful. Would like to keep the set up for the 40 under $250.