I have an attached spa with a waterfall feature into the pool. Overnight, the spa drains down about 9-12" (just above spa jets). I have opened the check valve made sure it was working and no foreign objects. I checked both suction and return valves as well, no foreign objects, seals seem to be in good shape. All the people I have asked, say it is most likely the check valve. However, I happen to have a ball valve that I can close and I did that, but it still drained. I am stumped. Any ideas from any of you experts? I assume the water is just draining back into the pool, but could it be a leak?