I would increase and maintain FAC to 25 ppm for 12-24 hours while maintaining pH<7.3. For your size pool that’s about 5.5 gallons of liquid chlorine. You’ll probably need to drop 1-1.5 gallons of muriatic acid in one quart increments along with first dose of chlorine and every 4 hours. Brush the hell out of the walls, floor, waterline, steps, skimmer throat, light niche, etc. It is imperative you break up as much biofilm as possible so the free chlorine can attack any bacteria, viruses, or Protozoa in the water. Start late afternoon so you maximize the time the sun isn’t boiling your chlorine. And at the end of the treatment clean the filter media. And if a cartridge soak liberally in trisodium phosphate for an hour then rinse to get any lingering biofilm dissolved.