The heater has been on for 24hrs in my 55-gallon tank set at 78. Now, the temperature fluctuates between 80.0 and 81.0 (I know that it is only a couple degrees). I bought this specific heater because of the great reviews it has received. My question is: "Is this normal for heaters to do this a couple days after they are turned on? Or is this heater broken?"
1degree variation is nothing really. How are you monitoring the temp swing(digital thermomoter) The size of the tank, size of heater placement of heater, Water flow around the heater,Lights, room temperature, all affect the temperature swing.
My house thermostat is always the same temperature 75 roughly. I have just 1 200watt Jager in my 46g tank Placed right in front of my skimmer pumps intake so the heated water flows threw the skimmer and gets distributed into the tank. It is set at 77degrees I measure the temperature using a floating glass thermometer it is at the 80degree line everytime I look at it. Really consistent. Very little swing and It really doesn't concern me if its 82 or 78 as long as it is consistent within 4degrees.
So I turned the heater down to 65 and it was still reading high 70s, low 80s. Then I turned the heater up to 84 and it's keeping my water temp right at 76 degrees (give or take 1). So I called up Drs. Foster and Smith and they were extremely helpful and friendly, and immediately shipped out a new one. So I go the new heater (exact same) in today and did the whole "calibration" or bucket test. The same thing happens. I set it to 78 degrees and it goes up to 88, I turn it down to 74 degrees and it goes to 84.9. I don't know what the problem is! Is it common for heaters to be off 10 degrees?!