I have black spots on my liner that look like algae – do you have any ideas?

Here are what the spots look like. What can I do to treat them?

Black Algae 2 Black Algae

Answer: Could be black algae, which is super stubborn. Get some Black Algaetrine and follow the label directions to treat the pool and get it right near that area. It could also be a liner mold which sometimes takes hold and grows through liners – treat for black algae first and let’s see what happens.