I've had problems for years with yellow algae. I finally started copper sulfate late last year. POOF! Gone.
Acid Wash then chlorine wash. You need to scrub. Take a read through the link below. Mechanical cleaning is needed to kill black algae. Prevention will be chemicals.
Swimming Pool Algae Information Page - Page 2 Algae Info Continued
And the Copper Sulfate works against black algae. The liquid isn't too expensive, but I think you can buy copper sulfate crystals and mix it up in water. If you need to worry about blue stains (while plaster) mix it in a 5 gallon bucket. I have a blue colored Diamond Brite "plaster" so blue staining isn't an issue. I pour it directly into water.