Off the top of my head evap could be caused by added turbulence due to extra baffles,smaller pump out chamber can cause extra heat,new fuge light could cause extra heat and the fan itself can cause extra evap. Somethings to think about

I have a fairly new thermometer that is out by 3 degrees. Unfortunately I tossed the receipt so I can't return it. It's the type that works of a temp probe that you submerge

Get several thermometers and make sure they all agree.

Place them throughout your system.

Unplug each electrical device starting with your heater(s) one by one each hour or so and closely monitor the thermometers. Unplug your return pump last.

OR it could be that with the added humidity in the general vicinity the evap rate is being limited thereby leading to an increase in temp. Solution? Open some windows.

Thanks for the suggestions. I'll be working on this in the evening and will post results. Or at least a picture of me using a Rio pump to beat the LFS employee who thought this pump was the right one for a reef tank. lol

Unplugged each device except the return pump. It didn't change much at all so I went out and bought a cheapo $3 thermometer and found the problem. The cheapo thermometer showed 76 degrees while the $38 digital one was showing 79.6. So I went and exchanged the digital for a new one... only to come home and find the replacement having the same variance. Retarded.

Nonetheless, thanks to all for the suggestions.