I have a 29 gallon tank planted with 5 gouramis, 1 red tail shark catfish, 1 pleco, and 2 clown loaches. The clown loaches are in there temporarily. I noticed a bad smell coming from my tank a couple days ago and I did a big water change and gravel vacuumed as much as I could. I have a HOB filter running all the time and also a big sponge filter running in the corner. So I have good filtration going. The smell went away mostly until I smelled again today and the smell is back but not as bad as before. Whats the cause? I've been feeding a lot of algae wafers lately. Could that have something to do with the smell? How can I keep the smell down permanently and what has worked for you guys in getting rid of a bad smell in a fish tank.