My bad. I was confusing this thread with another one.

If possible, you should check your sand filter for LEVEL and for QUALITY. Get a bag of LABELED filter sand from a pool store (NOT: Lowes or Home Depot). Open the filter and check the sand LEVEL and quality (gummy, lumped, etc.) If there's sufficient sand, and it's OK, remove a handful and dry it on a pan in the over. Place some sand from the new bag side by side on a smooth white cloth (old pillow case) with the dried sand. See if they are the sand.

Also if possible, replace the push-pull valve with a multiport valve. It will make managing your filter much easier.