Keep the chlorine levels at 15ppm - 20ppm until the pool totally clears. When the algae dies you will have a blue cloudy pool - keep the chlorine high until it is no longer cloudy. Run pump 24/7 and backwash (or clean cartridge) frequently. If you test 3X a day and raise the chlorine level and don't let it yo-yo too much it will kill it quicker.

How long will depend on a consistant high chlorine level and how much stuff it has to kill in your pool - might be one day might be 4 days or longer.