First of all, this is a great forum that I feel lucky to have found.
Second, I just ran into a strange problem with one of my Hagen CO2 cannisters. I started to notice a very potent smell around the aquarium and traced it to one of my two CO2 cannister. The smell is so disgusting it is hard to describe. It isn't the normal yeasty smell, but a greasy, petroleum, cheesy smell. At the same time, one of my black skirt tetras developed an eye problem. I pulled the offending cannister out of service, did a significant water change, and the eye problem immediately started to disappear. After several washings, the plastic cannister and the hose still reek.
This happened about one week after I changed the chemicals in both cannisters. I used the Hagen refill. The other cannister is doing just fine.
Eheim pimp club #23