Vedro2081

I had a Fiberglass pool installed last summer and shortly after the contractor was done with the work i realized that if i the spa is overflowing into the pool and i switch it back to only the pool my water level in the spa drops below the water level in the pool. It doesn't look like the water goes back to the pool as the water level is not going up. Weird thing is that if the pump is running and the spa is overflowing into the pool, the overall water level is not dropping. Can someone help with this? The contractor ran out of business shortly after i realized the problem.