Algae Problems

I took over a fish tank at the doctors office i work at about 6 months ago. Ever since then i have been fighting to get the tank up to my personal standards before i start filling with lovely expensive corals. My last issue that i am dealing with is a brown peach fuzz algae that just wont go away. I learned that this tank has been fighting this algae for over a year before i got the tank. I don't believe it to be dino because there are no air bubbles in the tips but it is coating almost all the live rock choking out all coraline algae. Ill attach some picture of it for your viewing pleasure. Now onto the stats and info of the tank.

Tank Size: 900 Gallon display with 250 gallon sump
Filtration: six 100 micron Large Filter socks changed very regularly
tub of bioplastics
fuge with cheato
Very large skimmer
Two Large Reactors filled with Carbon and Phosban
Large UV filter (Bulbs need replacing, working on that)
Auto Water change set to 15 gallons a day (this is a godsend)
Kalkwasser top off
2 RO/DI: one for freshwater, one for top off
12 Radion XR30w G3 Pro LED lights set to be on 7:45 to 5:30
Params: 8.2 Ph (currently trying to raise but its a big tank, takes time)
76 degrees
0 detectable Nitrates, Nitrates, phosphate, Ammonia

Stock: ~20 small/medium fish, ~6 cleaner shrimp, some corals, lots of crabs and snails

Feeding: 2-3 times a week mix of pellet, flake, and frozen

Any help with this problem would be greatly appreciated. Thanks again

-Phillip

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