Our 6 person spa loses between 1/2 to 1.5 inches of water per day until it reaches the lowest of the 6 jets.
It appears to lose only when I program the pump to switch twice a day between the pool and the spa. When I do not run the pump at all or when I only run either the spa or the pool modes over several days, it doesn't appear to leak. My pool builder has replaced all of the valves, including check valves, and has twice hired pool leak detectors and no one can say how the water is leaking out back into the pool. They are now telling me to keep the spillway on each day...but that just masks the problem.
The pump system is maybe a couple of feet above the pool level but about the same as the 18 inch high spa.
Any ideas? Thnx.