Do yourslef a favor,reverse the direction of your fan.IME,your much better off with active ventilation(fans)drawing cooler,outside air into your canopy blowing across the ends(w/flourscents,the majority of the heat seems concentrated near the ends) of the bulbs to vent heat off of them.Then use passive ventilation(vents,etc..)to allow the heat to escape.With passive ventilation,make sure you place the vents on top as heat rises and it will be most effective installed that way.
With halides or when you have high ambient temperature(>80F),the use of a fan blowing across the surface of water is best employed.This allows for increased evaporation thus cooling the water.
BTW,81 is not that bad.I run my tanks between 80F and 82F.In fact,there have been studies that have shown corals are much less likely to bleach at higher temps(86F+)when kept at these temps.Furtherrmore,its a much more natural temp to maintain a reef at,I think the average temps for the reefs around the world is 80degrees and in summer time,temps on reef flats can often reach 85F.