How do you get rid of black algae in your pool?

Two ways to get rid of black algae, algaecides typically do not work, mainly just a waste of money. First way is to spread either cal hypo or granular triclor directly on the algae. Lower Ph so the killing form of chlorine is more effective generally 7.0 to 7.4. You first should brush the spots with a ss brush. Do not do this on a dark plaster or vinyl liner pool, chlorine will either bleach or stain color. When doing this turn off pool sweep for a few days. Second and most effective way is to get two cases of liquid chlorine 8 gallons, and two gallon of ammonia hydroxide (most pool stores can order this for you) and muriatic acid. Close the pool for two weeks. Do not let anyone swim or animals drink from the pool for at least two weeks (diarrhea). Lower pH to around 7.0 Add the 8 gallons of chlorine around the pool. Turn on filter pump let run for 24 hours at least. Now you have to add the amonia hydroxide. When you do this make sure that no one hangs around the pool for a few hours (there are some gasses from the mixture of chemicals). let your system run as normal after the 24 hours. Brush pool with ss brush as often as possible. And make sure that the pool is not use. can not stress this enough. Wait till the chlorine residual has lowered to safe levels to reuse pool. At least two weeks. May have to add more chlorine after week one depends on the amount of BA, may have to try method one during this process. What this does is with the combination of ammonia and chlorine raises the residual to around 50 ppm and burns out the BA from the root. Once this is done there will or may be etching in the plaster from were the BA was, to help with this get a sanding block from your local pool store or professional, and sand the areas were the BA was to make the plaster more uniform.