I've used fans pointed at the water's surface before. It worked ok, it was on a smaller tank, a 29g i think, that was in my laundry room at my old apartment. It got really hot in that room.
I just had a small deskfan about the size of a 100mm computer fan. It kept my tank under 80* F. The room was maybe 80-85*f during summer.
From what ive read fans will only get you a few degrees of cooling. The main issue I had was evaporation. Every other day I had to top off the tank with a couple gallons of water. I was buying RO water so I didnt load the water with too many minerals or dissolved solids.
Alternative methods are to cool the room, or run a chiller.
I've read on some reef forums sbout guys putting frozen water bottles in their sumps when their chillers failed. It would bd a pain to rotate bottles out, but would work short term.
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