Growth on my Live Rocks

[ft1955]

I had my tank for over 4 years and all of the sudden I am getting a strange growth on my live rocks. Can anyone help me identify what
it is and how I could get rid of it. I took all ,my rocks out and scrubbed them, but they came back.

 

[P-Dub]

When you scrubbed them, what was the color and consistency of the substance you want gone?

 

[ft1955]

Beige and powdery