Mike, welcome to the forum!

Pop the top dome off (with the system off) and reach down and feel the sand, run your fingers through it - it should be nice and fluffy (wear a long sleve shirt to prevent fiberglass splinters in your forearm). You may just have a layer of 'crud' on the top of the sand, which needs to be broken up, or scooped out, if this is the case turn the multiport to rinse when you refire the pump to wash the stuff out.

What do you mean when you say "backwash" - the numbers you're giving indicate that you might not be doing it correctly - tell us what you're doing and we'll 'tweek' anything you might be doing wrong/ missing.

Again, welcome - we'll get you through this better than the pool store or Pentair!