If the fish does not float, it has nothing to do with hypoxia caused by high temperature. It may be caused by chlorine poisoning. Tap water cannot directly raise fish, and residual chlorine in water is very toxic to fish. Due to the high temperature in summer, in order to prevent bacteria from breeding, the waterworks will also increase the residual chlorine content. Baking soda (sodium thiosulfate) can be added to the tap water of fish farming to quickly remove chlorine. The trade name of this thing is Haibo or Yulebao. Just add it according to the dosage specified in the instructions.