which temp is right

Question
I have a 180 gallon salt water tank i have a thermom. in the sump and a chiller the thermom. reads one temp. and the chiller reads another which one is accurate or which one do i go by???

Answer
All depends it is possible that the chiller needs to be calibrated. Before you go through all of that, try to get another thermom. and see which 2 read the same. I would venture to say if the 2 thermom. read the same the chiller will need to be calibrated. Now if the chiller is after the pump you may be picking up some heat from the pump.