Did you mention what’s in your tank? A gradual rise to 85F would not harm several species. Key word gradual. Some maintain certain types at or close to 85. I have 2 cold water tanks, a 40 G with axolotles & a new 125 G purchased for my fancy goldfish. My tanks are averaging 77F lately. The goldfish are fine. I keep most heated tanks at 72-75F and the gradual seasonal increases are OK for my types of fish. They have never gone above ~77 from ambient conditions.
I take measures to cool the axie tank to no higher than 65F. I do this by insulating the windows near the tank. Closed blinds are not enough in that room. I have big pieces of cardboard & foam under & above the blinds to block out light. I buy cases of water bottles,$6 for 24, at Walmart. I remove the lids & pour out a little to prevent expansion in the freezer. Fortunately I have an upright freezer near the tank. I dump maybe 3-5 frozen bottles in the tank and replace them as needed and drop in new ones. I was prepared to buy a small window AC for this room, but it’s been unnecessary thus far.
I have inexpensive LED task lights for the room, it gets dark. Found some that use 4 watts, forgot the output, but enough to read by etc.
I have heard of people applying foam insulation to 3 sides of the tank to conserve heat & assume the reverse works to keep it out.
