I've had to wage war against black beard algae too. It is very stubborn, so be ready for a long battle. There are lots of variations on this method, but here is what worked for me. Each day for 5 days, take each plant and decoration out and douse them with peroxide. Leave out for just a couple of minutes, then place back in the tank. The BBA should turn grey, then vanish. Peroxide is harmless to fish and shrimp, and won't hurt the plants unless you leave them out too long.
There is a "easier" method, but there is more work on the back end: treat the tank with 10ml of peroxide per 15 gal straight to the water, then turn the lights and filtration off for 1 hour, for 3-5 days. This gets everything in the tank at once, BUT I found that it also messed with the nitrogen cycle and my Nitrites spiked for a few weeks before returning back to normal. So, lots of testing, water changes, and adding tons of healthy bacteria.
I also cut my lighting time way back to 7.5 hrs.
Good luck, and tell me if you find anything else that worked!
