You need to be sure you need to treat it first. Then you have to be very careful because a copper application can cause a DO crash. We have never treated our red plankton as it has not warranted such a drastic action. The one time I killed a bunch of BG was due to a limited CU application to treat a patch of FA when the alkalinity was low - the combo can cause BG gills to be unable to asorbe O2.