integrated spa water level dropping

There is a spa in one corner of my rectangular pool. It is at the same level as the pool. When the pump (variable speed) is on, the water normally overflows the spa wall into the pool, thus circulating the water. It worked great for 10 years. Now, the spa water level drops about 1/2" per day. It no longer overflows, and I end up adding chlorine to the spa as the SWG seems to only feed the pool.

I noticed that the check-valve is no longer full of water as it used to be, so replaced...

integrated spa water level dropping