Thank you John, your suggestion was right on target. I checked the sand level and it was below the requirements listed in the manual. Thank you!

As a sidebar, I bought sand from another pool dealer who was also selling "general purpose" sand as pool sand. The salesman was adamant that is was specifically formulated for filter use, contrary to the large font letters on the bag not supporting his claim. I didn't believe the poor guy, but took it anyway because the trip to Lowe's would have costed me more in gasoline than the high margins they had on their sand.

Thanks again John for your help!