Welcome to the forum.
I actually thought about two series filters years ago for the exact same problem of fine dust. Silt from my stream I use for fill water. Wound up throwing some DE in the sand filter and that works great. Can't imagine the little bit of DE would harm anything in your yard. This info was posted on the old forum before the crash. On a 300# Hayward sand filter about 2 cups of DE raises the nominal pressure about 1 psi. Trick is to calibrate the system. For the first couple times add a little DE and wait 15 minutes or so for the pressure to stabilize. I found it takes a little time for the pressure to stabilize. Keep adding in small increments until you get about a 1 psi increase. Once you are calibrated you can dump the right amount of DE in at once. I mix it with water in a 5 gal pail before dumping in the skimmer. Of course once you get rid of the fine stuff you can revert to the plain old sand filter mode. Two filters would work too but I'd plumb in a way to bypass the cartridge.
Hope this helps.
Al
(ajs-1)
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