bubble algae up front and what looks like bryopsis on the back Unless thats a feather duster (hard to tell)
emerald crabs help with bubble algae, but bryopsis is a different story. many times hard to eradicate! there are a couple treatments that may or may not work. first is fluconisole and the second is raising Mg in the 1500 to 1800 range. i would say get more pics of that fern like stuff in the back and post them to be sure before you venture into treatments.