I did some ghetto cooling on my 100g.
I had a ghetto sump made out of a rubbermade tub. this was the tall one because I could not fit in a long one, and fear of over flowing I chose the tall. I think it was something like 30" tall. maybe 27ish.
I had 2 overflows come in from the side and 90* across the top of the tub. (I drilled 2 holes on the top, side of the sump for the pipe to go across)
I put 2 PVC pipes through the side and drilled holes in it, slightly down from horizontal. this made the water stream out to the sides a good bit.
about 6 inches below I had my filter media which was pond foam sitting on egg crate. I had the lid on the tub, so I cut 4 holes in it. 2 for some fans I picked up at lowes that were AC power and about 4.5 iches diameter (more CFM then a computer fan, and only slightly louder). they blew straight into the path of the streaming water from the drilled pipes, and exhuast out of the 2 other holes I drilled that were on the opposite side.
this alone dropped my temp 4 degrees in about 10 minutes.
Now that I built a whole new sump and summer is rolling in, time to do something a little more cleaner, but the same idea.
blow air over the streams of water and something like a sponge that holds water and can be cooled. kind of like a radiator. | 
