Remove any parts of the hood possible. Do not turn off the filter as hot water means you need to get oxygen in. Lower the water level to let the water splash and add an air stone as both add oxygen and increase exaporation which lowers water temp. I asked this question about a month ago for a 10 gallon and tried all those things and they work. It's better to leave fish at a constantly hot temp for a short amount of time such as two or three weeks than it is to let it go up and down rapidly which stresses the fish.
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