How to calibrate heater and/or thermometer?

  1. superbutterfly12 Well Known Member Member

    So earlier this week I found my heater although set to 77 was heating my tank to 84 to 86 according to my floating thermometer. I've rearranged the tank and switched it to the other side of the tank, and adjusted it down as low as it will let me go, reading 71F on the heater but my thermometer still claims the tank is at 84F! How can I tell which is screwing up and is there a way to recalibrate them?

    36 gallon tank, Hydor 200W submersible heater, Marina Floating Thermometer
     
  2. bizaliz3 Fishlore VIP Member

    That's quite a big difference. I have tried many different heaters throughout all my tanks and most of them are inaccurate based on my thermometers. I never trust the setting on the heater to determine the temp. But they have never been that off compared to the thermometer.

    When I get a new heater I just pick a setting and keep a close eye on the real thermometer and when it gets where I want it, I leave the heater setting there. I have always just assumed that the real thermometers are perfectly accurate. So I trust them.
     

  3. superbutterfly12 Well Known Member Member

    Ok so you wouldn't doubt the thermometer just the heater? I have two other handmedown heaters. I guess I'll clean one and switch it out
     
  4. scottishduck Member Member

    My Hydor also runs hot. (and I've seen reports elsewhere on these boards on them as well).

    Unplug the heater
    Let the water cool to room temperature (as long as it's not too cold)
    Set heater to lowest level
    Plug in
    Notch up the thermostat on the heater until it turns on the light, then go back one setting
    24 hours later check temp
    Continue raising by one "click" a day until desired temp is reached.

    I have two heaters in my tank. The Hydor is set at about 73 through this method, the marineland (I think) is set to 75. The actual tank temp is between 77 and 79, depending on house temperature.
     

  5. superbutterfly12 Well Known Member Member

    Thanks I'll try that first!
     
  6. sunshine2012 Member Member

    What brand heaters do you have? I only ask because I have an aqueon and I was having the same problem and did some research and found out that if you take the blue turn knob off at the temp that it's saying on the thermometer without turning it and put it back on with the pointy part at the temp it's showing and then turn it down to the desired temp it should be fixed, it might be off a couple of degrees, but I could never get it to be exact. Hope that helps