Why is sand flowing into my pool, and how do I fix it?

Sand flowing into the pool is typically caused by sand that is too small, an overfilled sand level, or a broken skimmer. Use the recommended #20 silica sand (0.45–0.85mm), always stop the filter before changing the Control Valve position, check that the sand level is between the MAX and MIN marks on the collector hub, and replace the skimmer if broken. (Page 9)