Check Structural Leak Location
Using a Dye Tester, put a small amount of dye near suspected leak areas in the structure of the pool to see if the dye is pulled out of the pool. Check skimmers, return fittings, lights, cracks, main drains, and hydrostatic valves. Diving Equipment may be necessary for checking for leaks at the bottom of the pool. Hydrophones (an underwater microphone that attaches to an XLT17 or XLT30 Listening Device) can be used to check areas especially in concrete pools that can't be reached without diving.