Has anyone tried this? put a valve inline after the pump that allows water to be diverted to a setup underground meant to cool the water in the summer and warm it in the early spring. Being a caver I know that underground temps are pretty consistently the annual average temp. Here in the southeast that means 72 degrees or so which is cold enough to cool water or warm enough to warm. My thoughts were to dig a 5'x5'x5' square. Use PVC pipe to build a mini radiator that just uses 180 degree elbows like crazy to build as dense a pipe setup as possible in that 5x5x5 space. Fill with sand and cover with grass. Water be switched between bypassing this or not. PVC is probably not the best choice for conducting temps but I'm a bit fearful about using something metal due to rust. Salt pool.