Why is my temperature so high?

I've determined that my target temp for my Kuhli, Pleco, and ADF's should be
77-78f, but it's floating around 80-82, and I can't figure out why.

There's no nearby heat source in the room, and in fact I've shut off the
radiators in the room. There is a 75w heater in the 15g tank, but it's set
to about 75f. There *IS* a cloth covering the open part of the lid to
prevent the ADFs from jumping out. This may add insulating properties.
Ambient temperature in the room is 75f.

Can anyone offer insight as to why my tank temp is higher than ambient?

Is 82 this with a "Tolerable" range for my friends, or is this something I
should address urgently?


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The welfare of the people in particular has always been the alibi of
tyrants, and it provides the further advantage of giving the servants of
tyranny a good conscience.

- Albert Camus

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