LOW PRESSURE

[MWRENCH]

I AM HAVING A PROBLEM WITH VERY LITTLE FLOW FROM MY FILTER BACK TO MY POOL. I HAVE A HAYWOOD SAND JAGGUZZI FILTER. I CHANGED THE SAND LAST YEAR IT WORKED FINE ALL YEAR BUT NOW I AM HAVING THIS PROBLEM. IF I TURN THE FILTER TO WHIRLPOOL I HAVE PLENTY OF PRESSURE BUT IN FILTER MODE AFTER BACKWASH IT WORKS FINE FOR A WHILE THE THE PSI DROPS TO NEARLY NOTHING. =. WHAT CAN I DO???????????????