Planted Tank Guru
Join Date: Sep 2006
Location: Northern California
1) Use a drop checker like everyone else said. Won't give you a precise measurement of what your CO2 levels are, but will let you know if you're in the correct range. A bubble counter will help. I have mine in the 4-5bps range, but yours might be different depending upon tank size, etc, etc.
2) Don't use a diffusion bell. It's one of the most inefficient ways. Look up some ceramic disc diffusers or an in-line reactor. Those two are the two most common ways of injecting CO2. If you want, you can also look up Mazzei venturi injectors which cost a bit more, but also do a fantastic job of dissolving CO2.