Every 3 to 4 days I had to refill the pool as the water level was dropping below the skimmer.
I noticed that after the system had stopped. The water in the spa was dropping down from the over-spill level by several inches in matter of minutes.
The next day when the system started again the spa would fill up and the same thing happened. When the system starts then they are air bubbles coming out from the returns for a few minutes. Eventually the water level would drop below the skimmer. There is no evidence of leak on the equipment pad.
I marked the water level and turned the system off for 3 days. No change in water level, in the pool or in the spa. That ruled out a leak in the pool itself or the spa itself.
I found a 3 way valve and closed the spa return so that all of the water was going thru the pool returns. The pool level was then stable. So I thought I narrowed it down to the spa.
But I noticed something interesting. Although the spa return is closed, the water keeps dropping in it while the pool level is stable. Again, turning the system off completely leads to no level drop in either spa or pool.
Where is my water going? Why only when the system is being pressured? Why even when the spa is return is shutoff its water its water disappears?