What to do now? I cleaned the tank, filled it up and treated the water. Water was perfect. But my pleco did not survive that which killed all my other fish. He had white, cottonwool like growths all over suddenly and it just increased yesterday, so he died today. I am so sad. I want to know what do I do now - change all the water or just leave it to stand for a few weeks before adding any new fish? Thank you.