I wanted you to isolate the spa body and pool from the equipt. Then I can tell you where the leak is. If you do this test we can all chime in an trace it down. I think Tex is right, its those jandys. So lets find out.
Your spa suction valve is in the off pos for your spa but only your spa. From your picture I would like you to turn that jandy it to the right 90 . Not 180. If should be facing backwards. Thats turns everything off on that end. Pool, spa, the whole suction side.
Now nothing leaves your pump, and nothing enters it.
Do the same with your return line. Turn that valve to where its facing the filter pipe. The one labeled heater with an arrow. Your turning these valve backwards. Lift the handle a little to turn all the way.
Now nothing can leave the filter, or enter it. And noth can leave the pump or enter it. The equipt is closed
Fill the spa back where it should be. Let that sit over night with the pool /spa off. Make sure they stay off until you turn those valves back later.
Mark the spa body waterline and the pool after you top them both off with your normal water levels for each..
Then hit us back and tell us what water level dropped.