Sorry to bud in, but it seems I have the same problem with my 50g. After reading this thread, I've finally been able to identify the algae growth on my HOB intakes. I've had hair algae issues before, which I was able to remedy by getting a timer, to reduce my lighting to 6.5hrs. But I've never had black hair algae before. It looks like I'm gonna have to change the hours again and start dosing more.
So far the outbreak has been minimal, but I noticed that it's beginning to spread to my Amazon Swords. I better get on this before it worsens...
Thanks for the info!