It looks like some stuff I had in my tank before. If you get your nutrients in check the suff is pretty easy to pull off by hand. If the tank is large enough some tangs will eat it, my hippo and yellow tangs did, also maybe add a sea hare.
Using salifert test kits showing both phosphate and nitrate low. Started up a bio pearl reactor around 3 weeks ago. Tank is 120L. My lawnmower bleeny doesn't touch it.
Phosphate can be tricky to test for accurently, I would recommend a Hanna checker for that. Also, your phosphate could be low because of that algae so sometimes it's best to just use that as a judgement.