I maintain a pretty religious routine to keep my pool water balanced. It's a standard free form, chlorine pool around 18K gallons, with an over-sized Pentair cartridge filter, Pentair in-line chorinator, and Pentair variable speed pump. I run the pump around 16 hours per day year-round, higher RPM for 4 hours, and lower RPM for 12 hours. The pump cycle begins at 9AM before the sun hits the pool, so I have continuous circulation during daylight hours, and well into the night. I don't recall the speeds, but I based the settings on achieving 2 turnovers per cycle.
I've had 3 different pool companies test the water, and one actually said it was one of the best balanced pools he's tested. Chlorine, stabilizer, PH, Alkalinity, Phosphates, etc., etc., all in perfect range. So here's my dilemma; I continue to get green algae on the walls of the pool. Oddly enough, some of the algae is showing up on the shaded wall. None of the pool places has an answer, only to say that "some pools are just prone to getting algae regardless of chemical balance," which I'm beginning to wonder.
Is it possible that I don't have enough turnover/circulation? With a perfect chemical balance, could it be anything else?