I’m not sure what this is, but my best guess is that it is a kind of black algae. For the past half-year or so, this has started appearing on the aquarium plants’ leaves, the rocks, and other surfaces. Our Siamese algae eaters and Malaysian trumpet snails have not been able to get rid of it, but I think I have a solution.
I’ve been adding the recommended dosage of API Leaf Zone to the water for a month now, and the black algae has been going away. The plants are growing more and shedding any leaves that have the black algae on them. And as a bonus, the Malaysian trumpet snail population is booming! 😀
So, if your aquarium is suffering from black algae, give API Leaf Zone a try. It might just do the trick!