I setted up new tank. Dechlorinator added. Added safe start. Let sit for a week. Temp 79F Test subject Feeder goldfish First goldfish lasted 3hr water tested at store - not safe waited longer Second gold fish Mid day to next morning Tested again and said it was fine. Is it because water was too warm? I am planing tropical fish.(will add live plants maybe a potho) PS how long can a tank stay empty?