finch is right on. In order to kill an algae bloom completely you have to maintain a shock level of chlorine and let the pump running 24/7 for a couple of days till the chlorine level stays level overnight. Checking as often as you can during the day to get the levels back to shock. If it is true that you have no cya in the water, you will have to add bleach all day when the sun is shining as the sun eats up the chlorine that is not stabalized too. Finch is right, it can take up to a week for the cya to show up - add enough to get to 30, most people like to run their pool between 30 - 50.