What is this and how do I get rid of it

[afish70]

What is this on my tank. Tank is over a year old. I changed from T5 lighting to a Photon V2 48" a month or so ago and this showed up. No fish currently in tank at the time, had an Ich situation so all fish in QT right now. It is a 90 gallon reef with a HOB skimmer, and I am running GFO in a Phosban 150. Flow is from an Icecap Gyre 3K and a Hydor Koralia 1340.

Test results:
PH 8.2
Alk 10.82 dKH
Nitrate 0.0
Nitrite 0.0

Ammonia 0.0
Magnesium 1380
Calcium 500

Assistance greatly appreciated.

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[AlSimmons]

It looks like either Dinoflagellates or Cyanobacteria IMO. The link below might help.

https://www.reefcleaners.org/nuisance-algae-id-guide

 

[JUNBUG361]

What he said ^^