Black algae

[raj]

I bought Live rock from SWF and after a couple of months the rocks are covered by black algae instead of the coraline purple.
Why is this happening and what should I do??

29 G
T5/Actinic

 

[coraljunky]

Sounds like a form of cyano bacteria. Can you post a pic? You can remove the rock and clean it thoroughly.

 

[tarball]

Black algae is the nastiest algae you can have in a SW tank. worse then red algae. It represents very poor water conditions.
Tap water, direct sunlight in tank, overfeeding, lack of water flow, Crushed coral, lack of water changes, poor ventilation, high
water temp, bad filtration. Consider all these situation as the cause of red & black algae.