Brown Grass or moss

Sounds like hair algae. Have you tested your water? If so what are your parameters? I've always had good luck in the past by adding a lawnmower blenny. They love that stuff and will literally mow it down lol

 

Its interesting. I'll grow hair algae and have exceptionally low phosphate. (Skipping all of the technical reading and theories) best I can do now is either introduce a system or source that will consume the phosphate before the algae can or lower my photo period.
Here's what I can offer:
Photo period, keep it under 8-10 hr
Make sure you have good quality bulbs and not too old.
Stay away from natural sunlight.
Good quality skimmer rated for 150% more than your system volume.
Water change weekly for reef.
Feed a little more often than more less often.
Try GFO.
Try Ethanol (vodka) I prefer everclear. Has more carbon, less additives.

Best tip. Anything past good husbandry, change one thing at a time. Don't add activated charcoal, gfo and vodka all at once on an actively running system. If something goes wrong you won't know what. Also investigate each concept and learn as much as you can.

 

http://www.worcreef.org/index.php?PHPSESSID=8880743ba6260e9c7084bbca33b893d2&topic=14117.0

If you can identify which type of algae you have that is a good place to start. The algae guide above should help.