The rocks closest to my light are starting to get covered by what appear to be brown coralline algae. However I don't think it's coralline 
It's very flat and comes in round circular patches of brown.
It's a 40 breeder mixed reef that has been set up for about 4 months. I tested my water and my ammonia and nitrate are zero. I perform a weekly 10% water change using RO/DI water. I have no other algae problems in my tank. My cleanup crew consists of 2 turbo snails, two astrea snails, a nerite snail, 3 scarlet reef hermits, two blue leg hermits, an emerald crab, and a tuxedo urchin. They keep my tank very clean except for this new algae. They don't seem to touch it. Any ideas what it is and what could eat it?
It's very flat and comes in round circular patches of brown.
It's a 40 breeder mixed reef that has been set up for about 4 months. I tested my water and my ammonia and nitrate are zero. I perform a weekly 10% water change using RO/DI water. I have no other algae problems in my tank. My cleanup crew consists of 2 turbo snails, two astrea snails, a nerite snail, 3 scarlet reef hermits, two blue leg hermits, an emerald crab, and a tuxedo urchin. They keep my tank very clean except for this new algae. They don't seem to touch it. Any ideas what it is and what could eat it?
