At present I have a mini heater (7 watt) for my three gallon. The temps of our house maintain from 68 to 70 or so..I know these mini heaters only raise the water temp a couple of degrees...I have an outside the tank stick on thermometer...the two squares that are lit up are 71 and 75 degrees. I also have a 10 watt pre set heater (78 degrees). If I change heaters, what is the best way? Do I have to remove the fish and heat up the water with the new heater, or do I just take out the mini heater and put in the new one? Or should I let things be. Fish seems fine...he's active and is eating/pooping.