The 48g is 4' x 12" ? Is it an enclosed canopy ? There'd be room for four 4" fans, 3" for sure...? Two pushin', two pullin". Glass covers ? If so yank 'em ! Sump ? The frozen jug will surely help. Lot's of extra's though as they don't last long. I use 'em too butt it's a PITA ! Definately keep direct sunlight off the tank and if the room temp can be lowered, great.
More fans blowin' on the sump will help. Fans blowing on the water surface is the most economical method of heat reduction. The rate of evaporation will sky-rocket but that is the method in which the heat is removed.
I suppose you could wrap the tank with a damp towel and direct a fan on it, but that would look kinda' goofy now wouldn't it...
. Don't laugh, it's the best way to keep a six-pack cool when you're at the beach !
p.s. The longest day of the year has passed so don't worry my friends, soon it will snow...
