help with algae

[saltysooner]

I have noticed this brown encrusting algae on live rock and frag plugs. it doesnt scroll. tried using a brush on one of the frag plugs but it doesnt budge. but, it leaves a powdery substance in the bowl. thanks again.
in tank with flash

any suggestions or info is appreciated.

 

[saltysooner]

would a better pic help?