What is this?

[ravedood]

This green slimy stuff started appearing on my rocks. What is it? Should I be concerned since it is growing?

<a href="http://picasaweb.google.com/bgonzalez/Slime/photo#5188174869460396722"><img src="http://lh6.ggpht.com/bgonzalez/SAAZjj7LqrI/AAAAAAAABQo/73f_veuqLSw/s144/DSC00366.jpg" /></a>

 

[loyalrogue]

Blue-green cyanobacteria.

Treat as you would for red cyano... or any other nuisance algae for that matter.
Find the cause. Take away it's food and starve it to death.

Siphon out as much as you can when you do your waterchange.
Reduce your feeding.
Reduce your photoperiod.

If it gets really out of hand and starts smothering your corals, then use Chemi-clean Red Slime Remover.
It's not a permanent solution, but it will get rid of it for a short while.

 

[Osteomata]

Also consider increasing flow. Koralia 4 added to my tank and the red slime didn't come back.