None of my betta fish are in this tank, but it's annoying nonetheless.
I was going to be away for about two weeks. My Pearl Gourami, Rose Minnow, GloFish, and (at the time) three guppies occupied a BiOrb aquarium. Whatever feeder I put in there decenigraded(sp?) horribly... my minnow loved the food from it, so she kept it pretty clean, but it made the water smell horrible and now a nast film covers the lid and outside of the tank every few weeks, in which I clean it off that often.
My granpa got some for his tanks too... it ended up that he had to completely clean one tank out (the one with his Black Orchid betta), and the other two became ridden with algae. (Ridden... don't think that's the right word or way to spell it, but you get what I mean.)
I forget what brand it was... but I remember what it looked like and will never get it again!
My granpa says the feeder was probably made with calcium, thus the smell. And it's probably why my tank now gets unsightly dirty so fast.
Any good cleaners I can use to keep it from building back up? Or make it seem cleaner longer anyway :P