- Remove debris and test the pH level before treatment. Debris just soaks up the chemicals that you are trying to direct at the black algae, so skim as much dirt and plant matter from the surface as possible. Clean the skimmer basket and the pump's strainer pot. Test the pH level; if it is above 7.8, you need to shock your pool with large quantities of chlorine to lower the pH. Use a chlorinated liquid or a granular form of chlorine called dichlor. Be aware that the granular form can settle at the bottom and discolor a vinyl swimming pool. Add granular chlorine to the water in front of a return to avoid discoloration. Try to keep the pH level in the 7.2 to 7.8 range.
- Use a stiff-bristled nylon brush on black algae. You need to scrub vigorously to break the protective coating around black algae so that chemicals permeate the plant cells. After an initial scrubdown, treat the water with an algaecide that is designed to cure black algae. Don't skimp on the algaecide. Apply the pool product according to the manufacturer's dosage instructions. You want to add enough chemical treatment to get rid of all the black algae, but don't dump the entire contents of the bottle either. Like chlorine, a heavy algaecide load can discolor the pool.
- Run the circulation system so that the chlorine and algaecide get to all parts of your vinyl swimming pool. Clean the filter repeatedly as dead algae slough off and get caught up in the system. Don't forget to vacuum dead algae off the bottom of your vinyl swimming pool too. Continue brushing daily and reapply chemicals until you eliminate all of the black algae. Soak the brush in bleach to get rid of any black algae cells attached to the bristles. If algae are in the advanced stages, call a professional pool cleaning service to cure black algae in your vinyl swimming pool.
