To answer the OP's original question...

I struggled with a DE Nautilus filter for 15 years. The grids were sneaky in that a tiny, tiny tear would lead to mass amounts of DE flowing straight into the pool, as if I was pumping skim milk back in. After exhaustive visual inspection, I would usually find the culprit as a small tear at the edge of one grid where the two sides are sewn together in a seam. Since I can't sew, it was off to the store for another $30 new grid, sometimes more than one.

But truth be told, I never took all the grids out and stored them inside for the off-season, so likely I was just paying for my laziness each fall.