Came back from an 8 day vacay to find our pool looking like the proverbial Jolly Rancher. I had put 4 3" HTH pucks in the only-used-when-away inline chlorinator, so not sure why things got so far out of hand. Pool had been good until we left.
Anyhoo, I pool calculatored 15ppm chlorine as shock level for our CYA of 40, requiring approx 3 gals 12.5% chlorine (all further references are to 12.5% chlorine.) I figured that's what I'd do initially, then follow shocking instructions here to keep chlorine high until prob is gone. As a sort of 2nd opinion, my Taylor test kit booklet suggested algae removal process is to do a one-shot treatment of 30ppm chlorine or 6 gallons.
Sent my wife to the pool store to get a couple cases (had a couple jugs on hand also) plus a gal of muriatic acid as PH was around 7.9 and my Taylor acid demand test said I needed about 1/2 gal to bring down to 7.3.
She calls from the pool store and says the guy has a bit different idea. Puts him on the horn. He says we should immediately dump in 6 cases (24 gals) chlorine (enough for 125ppm chlorine). I asked how he figured that, like what ppm chlorine he was going for. He said, "I used 4 cases to clear up my 18000 gallon aboveground this spring, so you need more because your pool is bigger." Then he said, "And you need to add at least 6 gallons of muriatic acid to get rid of the algae." I asked what PH he was shooting for (that much acid would lower PH to approx 5.7!) "That's not what the acid is for. It's to kill the algae. You'll have to adjust your PH once the algae is gone." Then he sort of recommended using another algaecide, too, although he said it's too expensive. Plus he mentioned a flocculent because our cartridge filter would not be able to handle the dead algae and pooh-poohed the Sea Klear I had been using to control cloudiness (he may be right on that, we'll see in a day or so.)
She came home with 24 gal chlorine and 4 gal muriatic. I adjusted PH to 7.3 and dumped in 3 gal chlorine, tested chlorine using my Taylor K2005 kit and 4:1 dilution with tap water, and followed shocking recommendations here fairly well although perhaps erring on the too much chlorine side, using a grand total of 9 gal chlorine. By morning pool is white and cloudy but no longer green. Thanks TFP!
I do wonder how much trouble I'd be in if I had blindly followed along and got PH lower than 6. At very least I'd be rounding up 100lb of borax to get it back to where it should be. And I shouldn't knock the pool store too much as it does sell cases of chlorine for $10.99 and they're fresh because everybody around here buys 'em there.