big changes in temperature when turning off return pumps

[SeeFu]

I've noticed this for months now, but everytime I turn off my return pump and some of the tank water drains into the sump, I see a substantial drop in temperature. I can't seem to figure out why its doing this because at random times I'll measure the temperature near the temp probe in teh sump and also in the display tank and they're always really close (within 0.1 degrees). However last night when I turned off the return pump I saw a drop of about 0.6 degrees within a 12 min span. Is this normal?

 

[joseserrano]

All pumps give off some heat. Some pumps more than others.

 

[Copingwithpods]

Pretty normal, I think youre splitting hairs here