I've had the same thing this year. FC always 3-5 ppm, CYA 25-30. Water perfectly clear for 2 years now, never even a trace of green in the water, Never any CC. Small spots of green algae growing in the corners and in a few spots on the bottom. It brushes off easily, but comes back consistently. Shocked a few weeks ago to 15 ppm for 24+hours, algae back about 2 weks later. Phosphates tested at pool store at 3000-5000 ppb, home test indicates 2500+ ppb. Shocked the pool up to 20 ppm yesterday, dropped from 18 at dusk to 16 in the morning. Brushed thouroughly. No CC. Dropped to 10 today. Poured in 2L of Phos-free into skimmer of 13,500 gallon pool with 420 ft^2 cartridge filter, no rise in pressure. Tiny bit of cloudiness within an hour or so, clear again within 12 hours. Time to get in with the goggles and see if there is any algae still hanging around. Will test again for phopates tomorrow, see if the Phos-free did any good.