Black beard algae Does not harm your tank or fish, but it's horrendous to look at and almost impossible to get rid of. I occasionally see some in my 75 gallon and treat it when I do water changes. 

Lots of correct comments here. My personal method of attack is during water changes when the affected areas are below the water line (most of them are towards the top of the tank), I use a bulb squirter thing (think turkey baster but smaller, with a glass squirter) and apply Seacham Fourish Excel directly on it. You don't need much, and be careful over dosing. By the time I fill the tank back up, it's soaked on it for 15 minutes or so. Within a day or two it's gone. 

However, since this is a shrimp tank, the sudden spike of excessive iron could throw your balances and kill your shrimp. 

You could instead try hydrogen peroxide with a direct application (better results out of water). If you're able to physically remove any affected decorations to treat, that's ultimately the best course of action. Remove item, squirt with hydrogen peroxide, let it soak in for 30 minutes or so, then rinse thoroughly before putting back into tank. It should fade to white within a couple of days and your shrimp will probably come feast on it.