Red/Brown Algae (Bacteria)

[VO6]

Long story short, my reef has been set up for about 4 years. I’ve had many battles w Dino’s, hair algae, cyano, and bubble algae (still dealing w this dreadful algae, however, it’s being managed reasonably well w manual removal). My reef is a standard 40B w a HOB filter + HOB skimmer. I’m running 36” ATI T5’s (4 coral plus and 2 blue plus). I’ve always had an issue with maintaining nutrients, if I don’t dose PO4 or Nitrate (brightwell products) they’d bottom out - as of recently, they’ve been stable, PO4: 0.05-0.08 and NO3: 1.6-2.

My reef is a mixed reef w LPS (chalice, elegance, favia, blasto, goni, acan), SPS ( stylo, acros, monti, birdsnest), and some soft corals (zoas, gorgonian, mushroom, and leather). I recently acquired a maxima clam.

Fish include cave basslet, multibar angel, yellow banded possum wrasse, meleagris leopard wrasse, tailspot blenny, green mandarin, blue stripe pipefish, 2 green banded gobies, and a white tail bristle tooth tang.

My issue that Ive been dealing with is this brown/reddish algae (bacteria?) that gets all over the sand, rocks, and glass during the day, but “disappears” to the naked eye late in the evening whenever the lights are gradually turned off. Is it diatoms or cyano? I’m running 2 MP10’s so my flow isn’t an issue. I’m unsure what I’m dealing with, if anybody could chime in that would be great

 

[taricha]

Is it diatoms or cyano?

dino diatoms and cyano all are known to do daily vertical migrations that make them disappear and reappear from the sand during a daily cycle.
There's not enough color on the sand for me to guess what your nuisance is.