Each of the past 3 summers, my pool has "gone south" rapidly after the first signs of algae. Small whisps in a few spots on the bottom of my vinyl pool. I'd brush to encourage filtration or vacuum.
SWG, generally around 5-6ppm FC (0 CC). pH 7.6, TA 90-110. CYA 60-70. Pump running 10h per day...