Thanks again to everyone for helping me reclaim my pool from algae! It's taken me a while to complete the process, but I've finally SLAM-cleared the pool and it looks like my picture again. It's now completely clear in color, with only the faintest residue of cloudiness, which I hope to resolve today with another vacuuming. My last question is about how best to allow the chlorine level to normalize to a level that will be safe for people to get back in the water.
During the SLAM, I raised FC to 23-24 (CYA at 55-60) and held it there fairly consistently for about a week, although it always got a bit lower during the height of the day. There is a shortage of chlorinating liquid in town, so I did this by running the SWG at 100% 24 hours a day for a few days and strategically adding the only three gallons of chlorinating liquid (10% bleach) that I could get during the height of the day, when the FC level would drop. Levels varied between 19-24 during the day, and I also had to replenish CYA a fair amount, but I kept levels up as consistently as possible and backwashed the filter frequently.
Once the color was completely clear and the cloudiness all but gone, I ran and passed an overnight FC test (although I had never actually failed one, which was what made diagnosing the problem confusing). By the next day, the FC level was down to about 18, too high for swimming, so I'm letting levels drift down to a safer level and wondering the safest way to do that. In August, I would normally run the SWG for about 6-8 hours at 80-100% depending on levels. Instead, I set it to run at only 50% for 8 hours a day, to see how fast the FC would fall. Turns out, not so fast.
Three days later, FC is at 16, CYA: 55, pH is at 7.6, and TA is stable at 90. I'm wondering if it's safe to turn the SWG off entirely and just operate it like a non-SWG pool until the FC level normalizes, or whether this could invite another algal bloom? Does it matter how fast the FC returns to normal? And by the way, what's the highest FC level you'd allow swimmers in at? I'm always so grateful for the advice I get on this site--thank you in advance! --Erin
P.S. Dave and Carlos both noted the yellowish walls near the stairs and wondered what it is. The truth is that I'm not entirely sure. I can get most of it off by cleaning it with a magic eraser, but while that makes it much better, there is always some staining that I can't remove. Years back, my husband thought it might be mustard algae and he tried to get rid of it as though it were, but nothing much changed. Now my son and I just magic-erase it away periodically. The pool water is mostly rainwater, and very occasional some additional municipal water from the hose, but not recently. High TA, but no metals.
