ro filters and membranes are all fine. the bryopsis came in on a zoa frag i got from an unnamed vendor. the problem is isolated in only one of my tanks. i think i'll decrease the lighting cycle, keep the gfo running, keep the rock work blown off and clean, manually remove what i can, keep the Mg level around 1600 or so, and hope for the best.
i used the rite-aid brand of epsom salt to up my mag and kill of my bryopsis. it's food grade and it worked!
the best way, imo, is to fight a full front war: raise your mag, pick it out, and keep your po4 and no3 as low as possible. over time it should thin out
EDIT: oh and @gilmour: i don't think 1600 will cut it. i slowly let mine creep to 1750-1800.
gotcha...this morning i was at 2250 on an elos kit. i noticed my trochus snails were having issues, so i thought i'd see where i was at. LOL...i over-shot a tad.