It's really irking me. I have one 5 gal tank that despite water changes continues to smell moldy. I have 11 other 5 gallons set up right now and none of them have this problem. I have cut back on my substrate so can better see anything I need to clean out. However, all my tanks are like that and no problems with them. The water paremeters are normal as is the fishes behavior. I have tank additives like tetra safe start and Amequel plus I could put in but I though I'd ask here first. I know someone posted about this recently and I cant' find it.