Removing black algae will take equal doses of patience and persistence. If it's just the fountain, you can apply some chlorine and then brush the area. The brushing is just as important as chlorine (FC) in removing black algae. The brushing is necessary to remove the protective film that black algae forms in order to protect itself. Removing this film will allow the FC to work at killing the algae. However, I would test the pool water and post those results. It very well could be that algae is hiding somewhere else in the pool. Be sure to check behind pool lights and around ladders as these are some of algae's favorite hiding spots. Do not bother with algaecides of any kind. They are useless once you have an algae outbreak.
Once you post some test results, we'll take it from there. Also, a pic would be helpful.
