Dejital

I'm looking for advice. I inherited this hot tub system with my new house purchase. I had the electronics repaired to get it running, but it appears to be losing water. It appears to lose a half inch or so of water everyday. I opened it up to try to track down the leak, but as you can see in the attached video, there is no leak in sight. This is with everything running. The water appears to start halfway down the "foundation" but no clue as to how it gets there. I could use some help. A repairman couldn't find the source, and advised buying "Fix A Leak" to try and resolve it. And if it isn't clear from the video, the inside is actually dry. There are spots that are darker yellow and I assume they are from moisture underneath the tub. I touched the "floor" and it was clearly dry. Any opinions? Any advice?