algae. you need a sanitizer to keep it from growing!
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.
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
Trees above reflecting the pool.
Pool Shock
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.
The pool water is green because of algae- which is a type of plant. You just need to add more chlorine to kill off the algae...
I am not sure why this has not been answered. The most common reason for the green is algae growth. If you put on a solar cover and ignore pool maintenance, then the algae will grow as the water heats and when you remove the cover, the pool will be green
Green pool water is caused by algae. To remove the algae, bring the pH level of the water to 7.8, scrub the sides and bottom of the pool, shock the water with chlorine, then vacuum up all the dead algae.
Photosynthasis
If it is genuine 'black algae' it is very difficult to remove without emptying the pool and gouging the black algae out of the pool surface. Other algae can be removed by shocking the pool, filtering continuously and brushing walls while maintaining a good sanitizer level.