I was doing a 50% water change and despite my efforts to keep the temperature the same the temperature in the tank rose 3 degrees, will this be very bad for my fish if it happens every week? As the tank is a tropical one I can't leave it out to come to room temperature, because it would be much colder than the tank water. How do I keep the temperature constant? Do I have to resort to using an aquarium heater for the change water? cause I really don't want to do that. Oh yeah, how much of a temperature jump can fish tolerate if the water change is every week?