Three-5 degrees in 2 hours would be an excessive amount of. 10-15 levels in 12 hours could be an excessive amount of, Your room could also be heat but the tank water will likely be cooler, don't are trying changing things through including water or ice. Besides for preserving the tank in an additional part of the residence. A correct tank chiller or a heater is the one way to stabilize the temperature safely. An air condition might help, but I don't know should you particularly want it. So long as the water stays reasonably low most of the day, it is better for it to be stable then to soar even as you try to exchange it. What temperature is the tank water? I advocate you get an electic thermometer, that you would be able to get one for $3, then you are going to be competent to really know what the water temp is and the way so much it changes while you do water alterations, and that you would be able to measure the new water earlier than you add it.