| | Re: Do you HAVE to use CO2 in your tank?
Squawkbert has the right idea,
DIY CO2 can definitely be used, depending on the size of your fish tank.
However, even pressurized CO2 can be pretty safe if it is locked into a cabinet or in your aquarium stand. I haven't heard anything about CO2 disasters of this type.
To keep it child-safe I wouldn't leave anything exposed, just the little hose going from the needle valve or bubble counter into the fish tank. It can be made even safer if you are using a Canister Filter and have an inline reactor.
There are many plants that can do well without CO2, I have grown Water Sprite, Ludwigia, Java Ferns, Pellia, Giant Hygro, Bacopa, and Christmas moss without it. In fact, I still haven't used any CO2, my setup should be complete within the month.
I know all this information may seem intimidating, I didn't know anything 6 months ago. Read forums around for a while and you will definitely learn more than you ever thought could be learned about planted tanks.