In Miami Florida I have a 10K gal IG plaster pool, 35 years old. My problem is that green algae rapidly reappears on the bottom and sides soon after shocking with 2.5-5 gallons of 10.5% bleach. After reading advice here, I added PolyQuat 60%. Initially 12 oz, then 3 oz the next week. Still, when I sweep the bottom I see green clouds. Measurements: pH 7.4, FC 6, alk 70. Pinch-A-Penny measures pH 7.6, FC 4, alk 100, Calcium 230, Stabilizer 60, Phosphate 100. I use the pool only once or twice a week. I vacuum after I shock. There is a 70 square foot cartridge filter and a 1 HP pump. I stock the floater with two tablets of trichlor. I'm adding 3-6 cups of 10.5% bleach daily. The persistent green algae has been there for years and I'm getting very tired of it. I used to use a bromine solution weekly and that worked okay, but I'm trying to get away from that.