Strange alge

[ELChingonsReef]

Lately I'm getting this weird alge growing on my rock. It was originally dry marco rock . The tank is cycled its 9 months old I run a small UV sterilizer. Alkalinity is 8.3 cal 440 mag 1360 nitrates 9 phosphate. 03 PH 8.1 red sea reefer 300xl running raidon xr15 g5 blues on ABPlus program at 45% with whites turned down to 40% on acclamation mode with 30 days left. So the light intensity should not be the problem. It's mostly a lps tank torches acans etc.. 2 small sps frags

 

[ELChingonsReef]

It looks like it's a velvety dark brown or dark red alge. It's starting to cover the rock work. It started off one small pach now its spreading everywhere.