the truth is the ID doesn't matter. nobody would have a plan that changes to fix that algae based on a definitive ID
regardless of what you choose/discover, I'm positive that 1-2 test rocks need to not be allowed to continue as hosts. you have a 0% invasion option, it's simple external rock surgery. you can lift out those rocks and put them back clean using more than one creative means, some are very thorough and won't sterilize the rocks/we have neat ways of targeting algae and making rocks stay clean.
you can tell from the pigmentation there's a chance fluconazole would attack the algae but I don't recommend dosing it to the tank: the resulting dying mass circles you back to cyano and or dinos. hands off work leads to counter invasion delayed
hands on work means you can make at least 2 test rocks algae free, then set back in the tank in the perfect condition to chart how they compare to the other rocks and whatever method you're using on the rest of the rocks.
if this was a nano we'd just do them all, but large tanks often have unreachable scapes or locked arches etc, its crucial practice to at least be in control of a % of rocks in the layout so you have a method to fall back on
