Any idea what this algae is?

[BruenCuriosity]

A friend says it's juvenile bubble algae, but I'm still not convinced. Started growing maybe 3 weeks ago.
40b tank
Water parameters:
Salinity 1.025 (refractometer)
pH ~8.0 (API)
Temp 25.1°C (Inkbird)
dKH ~11 (API)
Calcium ~430 (API)
Nitrate ~5+ ppm (Salifert)
Nitrite 0 (API)
Phosphate <0.25 (API)
Magnesium ~1320 (Salifert)
Ammonia 0 (API)

 

[BruenCuriosity]

To note, the tank is young, but much of the rock and sand are not. It started off as a 14 gallon cube that I eventually upgraded to a 40 breeder. So, despite the age of what I transferred in, due to the size upgrade and adding more of, well, everything, the tanks been going through its new tank symptoms. Dinos and cyano have their areas but are receding. Did the upgrade a month ago.

 

[Subsea]

Consider Ulva.