For Concrete Pools: Black algae...the worst of all algae in the swimming pool to treat. This algae usually results from a prolonged absence of chlorine in the water. If the water goes green and stays green for an extended period of time...that is when it rears it's ugly
head(s)...spores of course. The algae have spores or heads which need to be brushed off with a metal brush to remove these heads (as much as manually possible) and then vacuum the swimming pool to waste. You want to remove as much from the pool water as possible, without putting the spores right back into the pool. Following this removal procedure you need to balance and chemically treat the water. This probably will not clear up the problem immediately, but it will start the process. Other options for removal involve draining, acid washing, chlorine baking, and possibly a re-surfacing of the swimming pool. These are more expensive and time consuming methods. However, if your swimming pool needs a new surface..that is the best option for removal. Here is a link on the web for you to view.