Tank temps

[outtafocus]

I seem to be having temperature issues with my tank.

When my lights are on, my temp sits around 79.5. The problem is when the lights go off, my temp fluctuates.
I check my temp when I first wake up, somedays the tank temp is at my usual 79.5(ish) but other days I will see the the temp down around 78.5, I find that when my temp is down low my heater is not on. I have also seen temps in the 80.4's up to 81, but my heater is on. The room temp stays farely stable and the tank is well away from any drafts or source of heat. These readings are all with no lights on.

I believe my heater is staying on to long but also not kicking in early enough.
Heater is an Ebo-Jager 150w mounted on an angle in my sump.
All of my pumps and powerheads and running all the time so its not as if a timed PH is adding heat.

Has anyone else experienced odd ball temps like this? Or found Ebo's to kick on and off at weird temps?

Any suggestions would be appreciated.
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