I have an Excel Pro 24" Sand Filter - less than 1 year old. I have just now started getting sand in my pool, definitely from the filter (CYA went straight to the bottom of the pool when poured in the skimmer). I took it apart and cannot see anything wrong with it - no cracked or broken parts, no channeling, 6 way valve appears to work as designed. I originally put 300# of sand in as directed. When opened it was only a little further than half way full. Can you lose much sand from backwashing? Why would it start failing to filter after working well before? Any help is much appreciated.