OK, after months with stable parameters (NO3 2-5ppm, PO3 .03-.08, Alk 7.5ish, pH 8.3, Ca 395, Mg in acceptable range, ICP tests confirm nothing out of whack) and not much positive to show for it, I decided to have someone look at things under a microscope. Thanks to @IOnceWasLegend for taking a...