Post split off from this topic by Moderator
If your CYA isn't too high, hit it with a few pounds of 60%+ granular trichlor, otherwise liquid chlorine. Though I used to absolutely gear away from all copper algaecides (except for last resorts) and will probably get heck from everyone for recommending it...well, it'll probably knock it right out! I'd follow up the super chlorination with a copper or silver-based algaecide, run the pump overnight, and re-chlorinate the heck out of it the next day, because the FC will get eaten up. You might want to follow up with a monopersulfate afterwards to clear up any remaining cloudiness from dead algae and CC. Once everything is trapped in the filter, clean it! Clean it good. This process is what I do in severe mustard algae cases, and works EVERY time. Don't get into a habit of relying on the stuff, though.
If your CYA isn't too high, hit it with a few pounds of 60%+ granular trichlor, otherwise liquid chlorine. Though I used to absolutely gear away from all copper algaecides (except for last resorts) and will probably get heck from everyone for recommending it...well, it'll probably knock it right out! I'd follow up the super chlorination with a copper or silver-based algaecide, run the pump overnight, and re-chlorinate the heck out of it the next day, because the FC will get eaten up. You might want to follow up with a monopersulfate afterwards to clear up any remaining cloudiness from dead algae and CC. Once everything is trapped in the filter, clean it! Clean it good. This process is what I do in severe mustard algae cases, and works EVERY time. Don't get into a habit of relying on the stuff, though.