ive been thinking of ways to regulate the temperature of a large amount of water. when i finally build something in the next five years or so, when i move into a purchased house, i plan to dig a trench leading away from the basement on the outside of the wall about 6-8' deep. through the wall will be an inlet and an outlet for 4"pvc. outside the wall, in the trench i plan to run a circuit of pvc, the ends of which will attach to the inlet/outlets in the wall. the idea will be to pump water out of the house, through the pvc, which will be buried and cool, and back into the house/aquarium system. depending on the locale, it could serve as a very effective cooling measure for whatever size system you have. id love to have a really big cold water octo tank someday. but i cant imagine its cheap to keep a tank chilled in the summer.