Algaecide in the water your pool shop will give you the right stuff I like copper based algaecide, and scrub the walls of the pool with a stiff pool wall scrubber on a long handle. you will find that a lot of the stuff will die and end up on the bottom after a day or so, Hand vac back wash and scrub the sides again. If that doesn't start to improve things you may have to use a floculent and then vacuum the algae to waste. Just ask your pool shop about it and the will set you on the right path.
You drain the water then plaster the walls from inside
Drain your pool, then scrub the walls and floor with pool cleaner.
Black algae shows itself as small black spots on the pools floor walls and fittings untreated they grow. Green Algae often starts as a greenish tinge on the walls or other surfaces of the pool and spreads into the water making it turn green if left untreated.
Aggressive water chemistry and age.
It may kill the algae but the algae needs to be filtered or the pool will remain green and cloudy You need to dissolve the chlorine and pour around the pool then brush the pool in order to not damage your plaster. This will help get the chlorine throughout the pool.
By killing the green algae with an algaecide available at your pool shop.
The sand filter wont make a pool green this happens a s a result of algae.
It might stain the plaster. When you have an algae bloom, get on it right away, don't wait. See the link below for more info.
By far the easiest way without a professional cleaner is a product called Pool Cage Plus. (www.poolcageplus.com) Shoots 25 feet to get the top of the pool cage. And you don't have to do crazy things like your pool brush and scrub it.
When a pool turns green, the cause is the build up of algae. To remove the algae, chemicals will need to be bought to restore the PH levels in the pool, killing the algae.
Algae
Shock the pool with chlorine (your Pool shop will tell you how much to add). Run the filter constantly, cleaning as necessary, for a couple of days. Brush pool walls as well. Then install a salt water system and you won't get that algae coming back.