Thank you for your reply.

Yesterday morning I checked the water level before turning it on and it hadn't lost any water. No air at all in the pump basket. When I turned it on it was fine, no air anywhere. Fine today, too.

There had been no backwashing the day before or any turning of the multi-valve. The only thing I can think of is that the bleeder at the top of the filter may have not been tightly closed. I would have thought I'd have seen water squirting out there, but it looks like only the filter was involved. When I saw the air I bled and tightened that valve so maybe that was it.

Still a mystery...

Vickie