I got a used aquarium for my daughter to start her fancy goldfish tank. Anyway, it was cheap because one side (a short side) is foggy or cloudy looking, but it's only cosmetic. The past owner had no idea what caused this problem. I've read that CLR or Limeaway may help, but won't that harm the fish? Does anyone know what causes this in the first place? It's not algae, as some people have suggested. It's that the glass itself is cloudy, even when there's no water in the tank. Thanks for any advice!