Algae = Phosphates. I don't care what your test kit reads. If you have algae you have phosphate issues.
Get a reactor and fill it with GFO. You will need a lot of GFO as you have a lot of stored phosphates. Change the media daily and manually remove the algae with daily water changes. GFO will last hours on a saturated tank not weeks or months as the label states. Once you have the tank algae free and phosphates under control GFO can easily last a month+.
There is nothing you can do to just watch the algae die. As it dies it pollutes the tank, if you don't have any gfo to soak it up more algae grows in its place.
You need a better skimmer. With a high fish load an 1/4 of skim mate you are not doing much and are better off running lots of carbon.
So to fix this issue you need.
-Fresh GFO in a reactor
-Manual Daily HA removal
-Skimmer and/or lots of carbon.
-Time
Also what are you feeding? Flake and Nori are super high in phosphates. The frozen foods ice tends to be full of it as well. Rinse mysis and such before feeding it. I prefer frozen formula 1 and 2 along with rinsed mysis.