air conditioners

Hello everyone! Wondering about what is the most efficient way to keep the water heated. If maybe keeping the ac on, helping the heater to maintain water temperature, i would get less energy consumption and less evaporation, since there is less difference between inside and outside water...

I live in a country where summers are extremely hot and humid. Temperature often hits 40 degree Celsius. If I turn on AC, how would that impact my cichlids? I usually do not keep the temperature below 20 degrees but is it okay for the fish? The tank and the AC are placed on opposite walls, but...