I have still had great luck with those 6 inch clip on fans from the discount stores. I have a 75 and tidepool sump and and a couple of 40 gallon tanks, fuge and sump system that stays in limits with one or two clip ons . if it was a real hot humid day i might have to run two all day, and one at night blowing under the home made light hood across the water surface, (no glass cover on the tanks), and perhaps one blowing on the sump and outfall of the skimmer. the 4 VHO's would bump the temp up to 82 by the end of the day, but overnight evaporation from the fan brings it down to 77. the temp swings dont seem to bother anything in the tanks. normally one per system is enough. none needed in winter as the house is coolerand dryer, and the tanks need the heat.
