bryopsis or diatom?

[FartyParty]

My friend set up a tank 3 months ago and recently had an algae outbreak and asked me to help ID it. After seeing it, i cant decide between diatom and some other unknown to me. Its covering all glass and rocks with light access (barely noticable in the overflow or sump) and is doesnt seem to have any solid structure (like diatom), but is solid enough to grow these wavy clumps toward the light (fungus-thick like). He scraped some off the front glass with a razor blade and it was blasted off in a fine, wavy sheet. I took a video with my phone, here:


What kind of algae or diatom (or other) do you think this brown stuff is?

Additionally, I brought my Hanna marine phosphate meter (not ULR) which read 0.0 one two different tests. His API strips read "zero" on both nitrate and nitrite, and his ammonia tag shows "safe" or none. Salinity was measured at 32 ppt and corals/fish/inverts inhabitants seem healthy, fish eating well, etc., from the 30 minutes i observed them.

Any help is appreciated! Im supposed to be his "fish expert" but have never dealt with this sticky stuff in my tank.

 

[Big G]

Is the "wavy" stuff filamentous or does it dissolve in your hand when gathered?

 

[FartyParty]

Id side on filamentous/stringy, but not thick like hair algae is. i get hair algae in my tank and its way thicker/stronger than this stuff is. He was brushing this stuff off the rock with a toothbrush and it seemed to be effective at removing.

 

[reeferfoxx]

Possible lyngbya. It's a filamentous cyanobacteria. Otherwise, chrysophytes. If manual removal doesn't work or gets worse, post the new picture. Should be more of a definitive answer by then.