I hate Bryopsis

[Mrfish55]

Water quality is most often to blame, regular water changes will help as will a lawnmower blenny or Diadema urchin, if you only have one or two rocks that are covered and you are able to remove them, you can freeze the rocks for min 48 hours to kill it and then scrub the rock clean (simply scraping or pulling it off the rocks will not kill it as it grows deep into the rock and will just grow back) I tried the magnesium trick once and it seemed to slow it down, but the regular water changes and a lawnmower blennie are what cured it for me. Good luck.