Freshwater Algae Question

[Foody]

I have a 10gal freshwater aquarium with a problem. I began noticing an "algae" growing off of the decorations about a year ago. It looks like hair algae but it is grayish black. Every month I do a water change (40%) and manually remove as much of it as possible. Every month it comes back. It is stringy and prolific. Any ideas?

 

[teamdulski]

I have never seen this algae before, but most black algae is usually associated with too much light, I would trim your light cycle.

 

[GMaquarium]

Black beard algae. Common issue in some tanks. Bleach the castle see if it comes back.