Good suggestions all. I'm gonna go with baking soda until I get a dehumidifier. I may get a small fan. I changed the water and it helped some, but I change the water a good bit. I know I overfeed in my 2 grow-out tanks, but I change the water in them 2X a week too. The room is a small one with no window, but I haven't noticed mold buildup anywhere. You know, I did notice the smell more when I got back from a trip and no one was going in there much. That could be it too.