Heater temp is different from thermometer?

  1. jbdub

    jbdub Valued Member Member

    Hi All,

    So I just got a Fluval 240 tank up and running and I'm seeing a difference between what the tank heater is saying and my tank thermometer is saying.

    The tank has been running about a week now so a bit confused :confused:

    Could it be because of the two big lights also raising the temp?

  2. c

    catsma_97504 Fishlore Legend Member

    Welcome to Fishlore.

    As heating is affected by all heat sources, this is very common. Room temps, lighting, even the amount of surface disturbance affect tank temps.
  3. Dino

    Dino Fishlore VIP Member

    Most aquarium thermometers are not very accurate.
    They are usually a degree or two off actual temperature.
  4. Jaysee

    Jaysee Fishlore Legend Member

    Also, where is the thermometer placed? Warm water rises, so whether you place the thermometer at the top or at the bottom will make a difference.
  5. OP

    jbdub Valued Member Member

    thanks for replies! the thermometer is at the far end of the tank, right in the middle.
    I had it in a smaller tank before and it matched perfect with that heater. It was only a 60ltr tank though
  6. i

    iZaO Jnr Well Known Member Member

    My heaters are off by 4 degrees in my bigger tanks. I just set the heater by leaving ot off for 30mins, then turning the dial until it comes on, leaving it until it reaches the temp i want, and then turning the dial the other way until it goes off. Then my heaters are set.