I have two 4-inch fans in my 72-inch canopy (with 3 X 250W MH and 2 X VHO FL bulbs). Since the VHO FL are plugged into an ICECAP 660 and a Solar 1000 dimmer, the VHO FL do not burn at full intensity so they are not a big power consumer and do not burn that warm. The fans are plugged into the same timer as my MH lights so they power up together. With these fans on during the day, my water has climbed to ~84 degrees. I also use an external fan that I wired up to blow across the surface of my tank. It really helps with the cooling, but also adds to the evaporation. The good news is that my temperature does not exceed 80 degrees during the day. It might be poor power management too, but it beats the crap out of buying a chiller and paying for its power consumption too. HTH
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