One thing you mentioned was Fiber Clear. This is not (despite what the pool store may have told you) the same as DE. I bought Fiber Clear last year to improve my sand filtration, I saw no improvement. I did see big clumps of what looked like wet newspaper on my sand when I opened the sand filter to winterize it. I don't kinow if Fiber Clear really works as a DE replacement in a DE filter but (in my experience) it does not work the same way in a sand filter - it appears to attract itself and just forms big clumps.

When PoolDoc says to use DE, use DE not Fiber Clear.