DE in pool

I have a 13K gal pool with a Hayward Micro Clear Vertical Grid DE filter (i.e. screens) 48 sq. ft. with a Hayward Vari-Flo control Valve (filter, waste, closed, backwash, recirc and rinse positions). The pool is 6 years old and I finally tore the filter down for the very first and only time after a battle with black algae to fully clean anyplace the dead algae could hide. Yes, my bad after 6 years finally doing the annual maitenance for the first time. During the first teardown I inspected the screens and saw nothing that I would take to be a problem. The screens all looked about the same, no obvious tears or holes anywhere. Anyway I reloaded the filter and then I noticed DE drifts in the pool, I guess 1/2 pounds worth total in the pool after a day or two. I tore it down again and double checked the screens (very detailed inspection) and the installation of the screens in the manifold and again nothing appeared to be a problem. Still getting DE in the pool, about the same amount. When I did the backwash prior to the first teardown the valve was hard to "break loose" to get to move.
My questions are:
Can the valve cause the problem, some leak providing a path to the pool?
Can the screen be "worn out" due to the long time with old DE on them?

Sound like the valve is a likely culprit. Easy to take apart and inspect the spider or wagon wheel gasket. It will be obvious if this is damaged. Something else to look for is water leaking out the waste line when in the filter or recirculate positions. If you do a quick search for vari-flow you should find lots of info. If not, post and we'll guide you. As for the handle being hard to turn, could be the shaft is gummed or the O-ring shot. Again, easy to take apart.
Al