I've never tried to reuse the magnesol but if Fabman has away, he would know he's THE MAN.
What I do is...after mixing I let it sit over night then pump the bio off of the top of the settled magnesol, that way I get several batches through my sock filters before I have to change them. With this method I don't bother with the 5 micron filters, I just use 1 micron sock filters.