For those interested in the results of fan based cooling power. Heres how it has been working out for me. I do not use a chiller and refuse to buy or run one.
2 fans on each side of canopy blowing into the tank: (I have holes in the top for the air to escape)
4X 80mm fans running requiring 0.16A each on a 300mA power supply. ( I didn't know any better)
House temp kept at constant 78 F
Tank temp prelight turn on 79-80
after 6 hrs of lighting 2x175w SE MH and 1 250w SE MH 82-83
I have the lights plugged into a Reefkeeper 2 that shuts all the lighting down if the tank hit 83 so i wasn't even getting my full 6 hrs.
after adding 6 additional fans pulling air out of the canopy and an appropriate power supply. 12V 2amp running a total of 10 fans @ 0.16A each.
House temp constant 78F
Tank temp before lighting turns on 78F
after 6 hrs lights on same as above 79.5 F max (never hits 80F)
Water evaporation before fans 5 gals every 3-4 days, now 5 gal every 2 days
With the reefkeeper the fans are set to turn off if the tank temp drops below 78F and turn on if the temp rises above 78.5 F the fans generally turn off a few hours after lights out due to tank temp drop saving elec and keeping a stable tank temp.
for what it's worth,
Quik