Which type of algae can penetrate into the plaster of the pool surface and cause damage?

Black algae is known for its ability to penetrate deeply into the plaster surface of a pool. It can form a protective layer that makes it difficult to remove from the pool's interior. Because of its strong grip, black algae not only presents a cleaning challenge but can also lead to surface damage over time as it colonizes and grows within the porous material.

While green and purple algae can thrive in pool environments, they do not have the same level of infiltration and destructive capability as black algae. Green algae typically grow on the surface, making them easier to eliminate with routine maintenance and chemical treatments. Purple algae, which is less common, has similar characteristics to green algae and does not penetrate plaster like black algae does.

Given this understanding, while black algae is famously known for its damaging potential to plaster surfaces, it's essential to recognize that the original question implied that various forms of algae can cause problems in pools. Thus, the answer acknowledges that black algae is the most damaging, and it reinforces the importance of monitoring and treating all types of algae for effective pool maintenance.