Yea that looks like ugly phase stuff on new rocks. I don't see it on the coral but...
on new rocks there's a couple possible things, silicate leaching out, and those are diatoms, as the easily dissolved silicate is consumed the diatoms fade. If its an algae feeding on Po4 bond to the rock its possible the same will happen, but generally you'll get cyano first. So if it blows or siphons off Id do it esp at WC time.
The ugly phase is caused by the silicate as stated above, and the the inability of the bio filter to process no3 and Po4 as larger colonies of good bacteria are not yet established. So other algaes cyano etc will take its place and consume it. So on thing to consider is bolstering the biofilter with a bottled bacteria like Prime, stability, Mb7, and Probidio etc. carbon dosing would do similar but the No3 is already pretty low.
This is also why its said young systems are not as stable. this is seen in usually higher nutrient numbers.
Def retest the Po4, maybe get a second opinion from a LFS with a different kit if its available. It is possible on of the rocks is leachin Po4 back into the system. no big deal, you can bolster the bio filter, and or use a little GFO to pull the Po off of the rocks. Poly pad, a bag of gfo int a decent flow area. I add GFO very slowly, as it strips the water fairly quickly and can effect corals.
Overall , nothing in that picture concerns me.
Keep in mind higher Po is feared because it increases the chances of fueling problem algae IF it is introduced to the system, and some corals don't like it and me effect overall health.
Heres a good thread with some stupid high Phosphate facts. The beautiful tank at the bottom had a Po4 of 3.0 not .30 btw.
https://www.reef2reef.com/threads/sps-high-nutrients-myth.283442/page-9#post-3460431
. Fwiw i've had no prob in this last year with high nutrints affecting GSP.
