I'm not really sure what's going on here.

The pump runs during the night and shuts off at 06:00. I'm generally up by the pool around 10:00 to clean the skimmer and PoolSkim and see that the pump pot is 1/2 empty. It used to be that the pot was filled to the very top of its domed lid with an air bubble the size of a quarter.

There is no evidence at all of any water leak anywhere. All the plumbing and the ground beneath it is bone dry.

What can I check or do to determine why the pump pot is losing water?