Jacuzzi at higher elevation to swimming pool, water falls off jacuzzi when pool filter running (is designed to do this!!). currently air bubbles coming from one of the jets when pool and jacuzzi turned off, draining jacuzzi into pool. supposed to, and has always stayed full, now drains to level of jet. What to do??

You probably have a check valve (back flow preventer) on the line that supplies water to the spa when the pool is filtering as normal. Your check valve may have some debris in it or the seal inside may have failed allowing the water to drain into the pool when the system is off. You should see a valve on the return line that splits off from the pool return line on your system. There are several different check valves on the market, some have a clear lid that you can inspect without taking it apart. Some of them cannot be taken apart. Your challenge will be to find the check valve, then try to check to see it debris may be holding it partly open or it the rubber seal inside is damaged or missing. I hope this helps.