well my 120 has been up and running for about 1 month now and i have a 300 watt marineland stealth pro heater. the problem is that i have it set for 86 degrees f and the led light turns green when my thermometers says its only 81 degrees. at first i thought my thermometer was the problem but i used 3 different and all of them read 81 degrees. so any thought would greatly appreciated. thanks