Wen, Scott, (welcome Scott, good choice comming here instead of being 'POOL STORED'), not only is getting the grids to fit in the upper manifold a hastle, if they don't all fit in tightly, de can pass through the gaps, and if that o-ring on the shaft that the manifold sits on is gone or compromised - de will go back into the pool. Another way for the de to enter the pool is by a bad seal in the multiport - in this case it only happens when adding the de, it slips by the gasket and some of it ends up in the pool. Yet another way is to have the pump pushing too much water through the filter for the filter to handle (somethings gotta give ). I'm trying to give the complete scenario. I, personally, prefer sand filters, but they don't clean as well as the others - though they are easiest to maintain. I don't want to tell either of you to replace the whole filter, but if you find you need to, get one with a multiport, you'll thank me. Any questions? - just post and I'll get back to you