Pool With Algae Getting Replasterd?

Hi, so I just moved into a house with an in-ground pool. We are going to get it replasterd this week. But theres algae on parts of the walls and on the tiles. The plaster guy is going to drain it but we don't know what to do. After he gets the plaster job done when we re-fill with water what's going to happen? Will the algae come back even though that plaster with the algae is going bye bye? I don't know how to backwash the filter It's a Hayward Sand Filter S244T and I don't know when to backwash. Can you please help me out? What raises P.H? Chlorine? Do i add stabilizer? What else should I know?