my water parameters are
Salinity 1.024
nitrate 20
nitrite between 0 and .5
alkalinity 240
Ph 7.8
phosphates .25
Mag 920
Red sea Mag titrate test
Mardel 5in1 test strip
API phosphate test
I had a hair algae issue a few months ago and was told to switch to RODI and add magnesium which long story short killed all my corals and all the algae.
Now the algae is coming back. I only use RODI and I dose with Kents Essential Elements in addition to a w/c every three weeks
I do 20G w/c at a time.
And I dose Vodka to keep my skimmer filled with waste (this officially works so i do it)
There also seems to be slight red patch of alage but its not the cyanobacteria slime type i used to see when i cycled my tank.
ENB
Nice aquarium! If It was mine, here is what I would think about.
I would get the phosphates and nitrates down, although this might not be your issue. So, it is one thing to consider doing.
Dosing with vodka is suppose to encourage higher populations of denitrifying bacteria, thus reducing nitrate levels. I wonder why your nitrates are so high. Is the test kit results off? I also wonder why you are still seeing nitrites a year after cycling. Again, test kit issues? Might not be contributing to algae growth but something to resolve.
A possible nitpicking thing. Your skimmer should be collecting a stiff foam and gunk if it is properly adjusted (water height, flow rate through skimmer). It should not need vodka additions to work. This might be a contributing factor to look into, not the root cause of hair algae growth.
I would make sure water changes are not adding nitrate or phosphates (test for nitrates and phosphates in the fresh saltwater).
Hungry snails would help reduce algae levels.
Hope these ideas are useful for your investigation.