Beginner-Novice

[daddy01]

Hi,
I have a 30G reef aquarium setup as room divider (small house), setup for a year and a bit, everything I have in seems to be fine I am running a overflose to a 10Gal (refugium/sump) with live rock and charcoal/phosban mixture and a skimmer. I turn the lights on sump at night after tank light go out.
Lately the last week I have started to get brown algae on gravel? I am running Two aualight flouresent light that give me 150W lighting. What is causing brown algae. (also using filtered bottled water for water changes)
Jim