Just replaced sand in filter (Doughboy media master). Before changing sand occasionally found small amount of sand in screen for polaris65. Now sand stops polaris from moving at least twice in 24 hour period. I have to blow out screen and replace, then all is well for a while. I bought sand at very reputable store, in business 20 years or longer. Before changing sand, filter tilted to one side, I assumed this was the cause of sand deposit. Filter is now level.
Also I recently replaced the valve cover due to a crack in the housing.