algae???

[lingtime]

this tank has been set up for many years. in the last couple of weeks ive noticed that i'm getting what appears to be algae on my live rocks. on my last change i scraped it off the "top" of the rocks and it appeared to have a white foamy substance under it. I've never seen this and my local fishstore seemed clueless. My water levels are fine, any ideas or remedies.

 

[ophiura]

Can you get a picture of it? What color? Do you have a nitrate and phosphate reading?
Many types of algae trap air bubbles. But it would help to have a picture of this.

 

[rcreations]

In my experinece, if there's algae, there must be nitrates or phosphates. Check your levels for these 2 params.