Blue color on Rocks

[bayarea510]

This past week I started to see a blueish grey coloring on my rocks, is this normal? It kind of looks like algae growth but it is an odd color. Thanks in advance.

[Avi]

It's hard to know just what you're describing from your description so could you post a pic?

[bayarea510]

Originally posted by Avi
It's hard to know just what you're describing from your description so could you post a pic?

Sorry all I have is the camera on my phone and it can't get the color clear.

[greenbean36191]

I've got some grayish blue coralline and sponges growing in one of my tanks. It could be either. If it's fairly smooth it's probably coralline. If not, it's probably a sponge.