I was wondering if anyone had heard of a company named Dennerle? I just bought a CO2 system from them and I'm not sure how well its working. Instead of a defuser the CO2 bubbles get pumped to a hood-type thing that is in the tank. They collect there and according to the instructions the CO2 sits on the water surface and diffuses this way rather than run the bubbles through the water. Anyone use a system like this? It uses yeast and a gel/sugar compound which is supposed to slow the CO2 production and make it constant but its only making something like 1 bubble per 1 or 2 min.