I have had ich in one of my smaller tanks before from what I believe is because I over fed it. But I've been paying close attention with my 20 gallon to make sure there is no over feeding. There is actually, from what I can see, no left over food on the gravel at all. My question is, what could be another cause of ich other then over feeding because I have no clue how my fish stumbled upon it. Also, only 3 of my cardinal tetras have it, none of my glow fish or dwarf gouarmies have any signs of it,(knock on wood!) All responses are appreciated.