Not sure exactly what it is, but it says to use it every week and you don't have to do a water change for six months. I didn't trust that claim, so I didn't go that route. Idk about hair algae. I'm pretty sure that's what's now in my shrimp tank. It came with my shrimp. The store let them live in a giant ball of it and some got caught in the net. Everything I read said it was caused by too much light and too much fertilization. But I hadn't even fertilized that tank when I got it and it gets barely any natural light, and the stuff was all over my filter intake cover and air bubbler.