Was just wondering how long tropical fish can survive without oxygen in the tank? I had a very bubbly tank but I was half way through doing a clean/change and the thing just stopped pumping. I have had a quick look and cleaned it out, which it wasn't too bad but it won't pump. I think it just may of overheated so have turned it off to cool it down. It was making a pump noise and was vibrating as if it was on.