Heater (82F) vs. Thermometer (75F) temperature reading. They are both different?

[Bubble_B0y]

I have a 40 gallon tank.

I placed the heater next to the filter and set the thermostat to 82F.

I put a thermometer on the other end of the tank, which gives a reading of 75F.


Is this discrepency normal? which reading do I trust?
Is my tank too cold? Should I increase the heater thermostat
I have 2 power filters and my tank is covered with a lid. Am I losing heat?

I have angelfish, gourami, corydoras and tetras.

 

[slitherbomb]

You should have 2 heaters at each end.

 

[ocean]

What kind of therm. Are you using? If it is a stick on they aren't much good. I usually place my heater in the middle (back) of the tank, so it's almost touching the substrate. Might not be correct but works for me!!

 

[BillD]

You can't always count on the thermostat on the heater to be accurate. Some brands ( like Eheim) can be calibrated to reflect the correct temp. the accuracy of the thermometer also needs to be checked.