I have been using a Tetra CO2 diffuser ever since the March ice storm clobbered my Crypt tank. It works pretty well for me. Sometimes the top bell jar fills with air other than CO2 and I have to empty it. My tank hasn't recovered as well as I hoped but I don't think that this is from the Tetra kit. What problems have other people had with them? I wasn't aware of any. Gerry Skau ANS Communications