I described my tank in my profile, but I'll write it out again.
So I have a 20 gallon tall aquarium with a hood and stand. It's set up for two Axolotls, but I haven't purchased them yet--I'm waiting until I get this problem solved. So I have a tank divider in the center, and on one side (the left side) is the Aqueon Pro 50 Watt heater, and on the other side is a Fluval U1 underwater filter (meant for 15 gallons but I didn't want anything more powerful than that to stress the Axolotls out). The problem is, that with the light AND heater on (heater set at lowest setting, 68 degrees f), the tank gets up to 74-75 degrees! Before I had a different thermometer, the kind that you stick on the outside of your tank and whichever number is lit green then that's the temperature of the tank, but with the setting at 68, I thought that had to be incredibly inaccurate so I went back to work and bought a different thermometer (similar to this guy http://www.petsrising.com/acatalog/F...SmallImage.jpg
). And it also showed the temperature as 74-75 degrees! That's WAY too warm for the Axolotl's, and 68 degrees would have been perfect! I don't know what to do now. I turned off the heater and put a ton of ice in the tank to drop the temperature, but I'm afraid that I wont be able to have it stay at 68 (it's at 69 now). I made a little chart today that I stuck to the side of the tank to keep track of the temperature throughout the day (writing down the day, time, indoor and outdoor temperature, and then the tank's temperature).. I'm just really disappointed that the heater is overheating my tank. I don't want to keep wasting money on heaters if they're not going to heat it to the temperature I'm setting it to. Help please!