Detritus or Algae or Bacteria

[vidruma]

I am new to Saltwater/Reefing. Just setup/cycled my first tank (~65-gallon Red Sea Reefer).

Tank is fairly empty right now with some live rock and two clown fishes. Tank still has some nitrates (25ppm) and very minor traces of phosphates. These are essentially remains from tank cycling (even after initial 40% water change); parameters have been very stable for now and I plan my next water change in a week.

Question:
Can someone tell me what are these brown spots on my rocks? The started showing up few days ago and today I see couple on the glass as well. Not concerned too much ... mostly learning. Is this Detritus or Algae or Bacterial colony of sorts?

 

[vidruma]

Just saw another thread with pictures similar to mine. https://www.reef2reef.com/threads/start-of-coralline-algae-or.954715/


So likely Coralline Algae then?

 

[bushdoc]

Those are not coralline algae, but most probably Diatoms ( let's hope).
Diatoms are usually first algae appearing in new tank.
It takes months for coralline algae to start appearing in your tank and usually they start on powerheads, overflow and glass. BTW, is it live rock? Looks like dry rock to me.

 

[vidruma]

Thanks for your input.
Diatom makes more sense. Seems like they are pretty common in a new tank, also the current levels are not much of a concern here.

Yeah, technically these as still dry rocks and it would take them months to be classified as live.