Six year old sand filter (Hayward s244t). This season I've been getting lots of very small tree particles in the pool. I have very large oak trees on 2 sides of my pool. The particles build to the point that my vacuum filter clogs and does not move (Polaris pressure side 165). I cleaned the sand filter yesterday by gently moving water hose thru sand (low pressure on hose) then let the filter fill and drain from the top for 10 minutes> I'm still getting the particles in the vacuum and pool. I did not drain the filter from the the bottom drain before starting cleaning. Do I need to drain first before cleaning or just clean for a second time since the filter has never been cleaned ?? THANKS !!