tthe only reason i wouldnt use ice coolers like a bottle of frozen water, is just the maintence value. I dont see a pump making your res temps rise signifigantly, i used to run a pump 24/7 in 5 gals and it made the water feel warmer, but it really was a temp difference of about 8 degress about 69 room temp, water always is cooler then roomtemp left alone, i have always found the best bet leaving the res on the floor, i dont think the pump is the problem so to say it contributes a little bit, better cooling methods other then off time on the pump is your best bet like suggested put it on the floor, out of the light, insulate it, these all help out alot more.