If algae start to grow, then your pool water quite likely lacked chlorine. To get rid of algae effectively, add chlorinated shock treatment and destructive algaecide. Wait three hours and then brush the walls and the bottom of the pool. Wait 12 hours and vacuum to pick up the dead algae from the bottom of the pool. Then do a backwash.
Note: A slippery pool liner is a sign that algae are beginning to grow.