If chlorinated water is the main culprit, there may be two things which can be done simultaneously.
One is to get something which would neutralize the chlorine in the water. When I was in school, I have tried Sodium Thiosulphate successfully. Just check with your nearest tropical fish shop to see what's available. The other thing to do is to start storing up water in separate containers. Usually after three days, the chlorine in the water would have dissipated. Then use this water to change that in your aquarium. If you keep on adding fresh water from the tap to your aquarium and chlorine is the main culprit, it wouldn't solve any problems.
As for the question of temperature, I have used a small fountain before to solve the problem. When the water goes up in the air, it cools down very fast. Then when the cool water falls back into the aquarium it would help to bring the temperature down. If you cannot find a ready-made fountain, you can make one by modifying a small water pump, the type used to filter the water in the aquarium. All you need is to add a spray head to the outgoing end and you are all set. Make sure the incoming end is properly shielded with a net so as not to suck any of the smaller fishes into the pump.
