How do you clean a pool that has flock added and a low PH balance?

Flock only works when the PH is above 8 (most pools are around 7.2 - 7.5). You have to raise the PH BEFORE you flock. I just did this very recently. My pool water had turned completely green, you couldn't see the bottom. I raised the PH (took and about 2 hours) then added the flock. Let the pump run on recirculate for 4 hours then turn it off overnight. Vacuum to waste, very slowly. This does involve topping off the water in the pool, letting everything settle down then vacuum some more. My total vacuuming time was 5 hours, but the pool was just a little cloudy when I finished, but no green water at all. It was worth the time and trouble to use the flock since I had been trying to get the green out for over a week, with no results. My algae was due to a construction project around my pool and granules from the new roofing got in the pool. The acid from the granules caused algae to grow very rapidly. That is what my pool dealer said to do and it worked great. Hope this helps.