Skimmer lids blowing off

[JamesW]

Is water draining from the spa to the pool (through the skimmer lines)?

That won't blow off the skimmer lids.

This requires explosive decompression.

Basically, only compressed air will blow off a skimmer lid.

Unless a different cause can be definitively proved, then I think that air compression is the answer.

 

[Bill1974]

I am at a loss. Some where there is a restriction in plumbing and there is a pocket of air that gets pressurelized. Once the pump turn off the path of least resistance is back through the skimmer lines. To pop off the skimmer lids that would be a good size air pocket or some pretty high pressure. Maybe all the return lines are collapsed? I am guess everything visiable is fine. Back flowing through the pump is pretty resitictive, I can't imagine backflowing enough to pop the skimmer lids off. Maybe the filter is almost completely filled with air?

How about some photos of the pool, spa, plumbing, etc and a video of the lids popping off.

 

[Mayorb]

Is there a height difference between the spa and pool? Is water draining from the spa to the pool (through the skimmer lines)? Lazy check valve

At this point I'm not ruling anything out, other than a suction leak. The spa is raised about 2 feet, but not losing water back to pool overnight. The high back pressure is sudden. I still haven't been out there at the time the pump finishes it's daily run.