Algae happens. Maybe you feed heavy or you have a couple of dead spots in your tank. Emarld crabs work great on hair and bubble algae. If you go this way, investigate the emralds at night because once they eat all it up, they tend to eat polyps. I store mine in my sump and feed them algae pellets once in a while, if the dt has some algae growing in it, it just put them up top and a couple of days its gone. Beaware....... Crabs are farting machines! You can smell the fart bubbles!:-)