Hi I have had my tank running lovely so brought 2 clown fish which i thought was a good one to start with! within a week had white spot, used what the shop sold me, but kept on coming back and a lot worse so last night they were so pale and both died, had them for 4 weeks now upset and not sure what to do, how do i know the tank is clear? I have done a part water change but don't want to buy anymore if the germs are still in there... all tests are ok. Help