If you have recurrent algae despite a chlorine of 5, then you have a bloom somewhere that has not been completely killed off. Shock your pool up to about 15 ppm, and hold it there until there is no more green algae by testing 2-3 times during the day and adding more bleach to get back up to that 15 ppm. Brush it daily, as well. Once the algae is all dead, you can filter it out, and as long as you maintain your Cl at least 3-4, you shouldn't have problem with it coming back.

Janet