Cant figure this one out. Help with ID

[Phistergosh]

My tank has been up for a few months. paramaters are all good so i wont list them. I started with half live rock from an established system and the other half of the caribsea purple reef saver rock. I ended up adding a few pieces of caribsea normal white dry rock after a month. then i added a little more rubble pieces for newly acquired frags a month later.

i have brown spots appearing on all of the white dry rock i added. ive never seen this and cant find anything in the ID guides here and on other sites. The spots were very small 5 days ago and have progressively grown every day. the spots cannot be brushed even when doing so aggressively with a toothbrush (makes me think its not cyano or diatoms. will try my wire brush if i cnt figure this out. the spots are only showing up on the white dry rock i added a month ago. the more recent rubble pieces, the purple dry rock, and the live rock dont have this from what i cant tell. my CuC isnt eating it (full crew form reef cleaner). It seems to grow better in full light and with decent flow.

Any clue what these are?

 

[Suohhen]

Looks like turf algae. Not typical to see on dry rock so it likely came from the established rock. It is typically a slow grower but given the lack of competition maybe not so slow. Theres other algae there as well. I wouldn't worry too much, things need to run their course. If it gets worse or bothers you go ahead and pull the rock and spot treat with hydrogen peroxide.

 

[Phistergosh]

it doesnt seem to be growing vertically and spead very fast throughout the tank. none of my cleanup crew seems to be able to remove it. I have nerites, dwarf cerith, florida ceriths, and various hermits,

 

[Suohhen]

Only larger inverts such as Emerald Crabs, Urchins and perhaps Mexican Turbos will touch the stuff. I generally don't recommend keeping these as it certainly hasn't developed into a problem and there are ways to keep it from. I would say however that you might want to consider adding an Astrea or Trochus. Reef Cleaner CuCs are way oversized for an aquarium but the crew you have specializes in different things. Nerites tend to cruise the glass, cerith chill in the sand, and hermits cruise all over but they are more of a scavenger and there is nothing quite like the bigger snails. But yeah start small, maybe 1 or 2.