Hello. New here to the forum so please be gentle 
. I live in the Buffalo, NY area. Have a large, vinyl-lined inground pool since Labor Day weekend 2020. Last two years have had to deal with very stubborn brownish-greyish-yellowish fine dusty algae. Opened this year on May 8. Since then, have shocked pool along with Yellow Out accelerant (following instructions exactly), and copper-containing algaecide, 6 times. Each time using 6 x 1 lb bags of shock. Pool is approx. 24,000 gallons. Heyward salt system cartridge, size C200S. Alkalinity and Ph are balanced. Phosphates at 0. I use skimmer socks. Pool is crystal clear other than mustard algae along liner seams, deep end floor crease, and other areas where it keeps spotting. Can't vacuum to waste as Heyward cartridge filters do not have this feature. I clean the cartridge with high-pressure hose nozzle every 2-3 days. Clean skimmer socks every other day. Only thing that has gone in the pool since opening are the robotic cleaner and the brush pole. Algae was in pool a day after it was professionally opened and shocked the first time. Same thing happened at opening last year. From what I understand, this type of algae is chlorine resistant.
Any and all advice on getting rid of this nuisance is appreciated. Thank you very much.
. I live in the Buffalo, NY area. Have a large, vinyl-lined inground pool since Labor Day weekend 2020. Last two years have had to deal with very stubborn brownish-greyish-yellowish fine dusty algae. Opened this year on May 8. Since then, have shocked pool along with Yellow Out accelerant (following instructions exactly), and copper-containing algaecide, 6 times. Each time using 6 x 1 lb bags of shock. Pool is approx. 24,000 gallons. Heyward salt system cartridge, size C200S. Alkalinity and Ph are balanced. Phosphates at 0. I use skimmer socks. Pool is crystal clear other than mustard algae along liner seams, deep end floor crease, and other areas where it keeps spotting. Can't vacuum to waste as Heyward cartridge filters do not have this feature. I clean the cartridge with high-pressure hose nozzle every 2-3 days. Clean skimmer socks every other day. Only thing that has gone in the pool since opening are the robotic cleaner and the brush pole. Algae was in pool a day after it was professionally opened and shocked the first time. Same thing happened at opening last year. From what I understand, this type of algae is chlorine resistant. Any and all advice on getting rid of this nuisance is appreciated. Thank you very much.
Okay, so you've been pool-stored and tricked into buying several products and using techniques that not only do not work, but may have cause more damage than good. Copper for example. Copper has no place in pool water. Once in, it cause very bad staining and hair changes. The only way to remove copper is by water exchange. But don't panic just yet.