Help Identifying Brownish Patches on Substrate

[RYcube2951]

My mature reef tank has brownish green patches in the CaribSea black sand. Also some green film on the glass near substrate. Can anyone identify this algae or bacteria and offer advice on how to remove it. See photos. Thanks.

 

[shakacuz]

seems like organic matter buildup turning into algae. slightly increase flow, or increase your clean up crew, or specifically an invert that stays in the sand that can help clean it(cerith snail, nassarius snail, sand dollar urchin, fighting conch, tiger/strawberry conch)