Temperature/Thermometer Readings/Differences

[oh207]

Hi MR,
For the past few months I've been using a digital coralife thermometer to monitor my tanks' temperature (cost about $7). The probe is sitting in the DT just about 2 inches under the return line.
Today I hooked up my Apex with the fancy temp probe and it is registering the temperature exactly 2 degrees less than the digital coralife thermometer!
Coralife is showing 79.7 and Apex is showing 77.7.
Which one is correct? I wouldn't mind if the temp is off by 1 degree or a fraction. But its off by 2 whole degrees. Is this normal? Should I get a third temp probe to confirm?
If I settle with the Apex readings it will affect other programmed settings such at fan(s), pump speed, and light.

 

[edd]

i dont know about apex, i have an rkl and you have to calibrate the probe occasionally. i use a quality mercury thermometer.

 

[oh207]

i dont know about apex, i have an rkl and you have to calibrate the probe occasionally. i use a quality mercury thermometer.

I didn't see an option to calibrate. After thinking about this some more I realize I have the coralife probe in the DT but the Apex probe is in the sump. I don't think this should make a difference but will put the probes together to see if they register the same or still different.

 

[MatthewScars]

Buy 3-4 little crap glass floating thermos and take the average temp, then set the apex to that.

PROBLEM SOLVED!

 

[oh207]

Buy 3-4 little crap glass floating thermos and take the average temp, then set the apex to that.

PROBLEM SOLVED!

Good idea. I already have one of those and will use it to double check the readings. I think I need to first determine if the temperature is actually that much different in the DT than it is in the sump.
I plan to do so my placing everything together in the se area and register the readings.
I also think that the placement of my heater affects this. My heater is currently in the overflow chamber. I might have to move it to the sump.