I've experienced the same issue, especially the hair algae in my moss. It's from too much lighting. A few squirts of hydrogen peroxide directly onto the effected area will take care of the problem. I actually spot treated my moss tree yesterday. Simply use a dropper and squirt it onto the plant in the water or remove it out of water...does not harm to my shrimps or fishes. The black bearded algae will disappear on its own but the hair algae in the moss will die but may need to be removed manually.