looks like diatoms. if your tank has been cycling for 2 weeks (the brown part). But what is the Really dark part of the rocks? Where did you get the rock from?
i bought the rock from marco rocks or reef rocks i forget, but I got it dead, i seeded it with a 2lb rock that i bought from Feng down at the Red Sand in Dunellen NJ.
it was white when i got it, now 2 weeks into the cycle and its turning brown, all im asking is if its normal for this to happen, or if somethings going wrong.
I had similar issue few weeks ago, I ordered a large clean up crew of snails, hermits and an urchin. My rock looks a lot better. You have anything on glass yet? I waited too long and it spread to my glass but the crew took care of it all. I used reefcleaners but there is a bunch of place to get a cuc
I see in that pic the brown diatoms on the right side of the rock. What is that color where it is not brown? Maybe just the picture?? Is that a total shadow maybe that is making it look black/dark...