Well I don't feel I should give YOU advice as your tank is cleaner than my ever has been
. But if it was me I would be trying to figure out what has
changed. Algae typically is not a big mystery, it is a plant that given the right conditions will flourish. Light and nutrients are what it needs. If it is a new occurance it is likely something changed giving it an opportunity to start propagating.
So . . .
Has the flow changed in your tank e.g. a new rock or coral was added, disturbing the old flow pattern? or is the system getting older and the pipes are calcifying and restricting flow? Maybe the powerheads are getting a lot of coraline that has reduced performance?
Are you feeding a different food? have you added bio load? Have you removed a rock to make room for more coral and shifted the balance?
Have you siphoned detritus out of your sump recently, what about the overflow boxes?
Is your skimmer perhaps not performing as efficiently (time for a vinegar bath for the whole unit)?
When did you last replace your bulbs? Bulbs change spectrum as they grow older and can start algae growing.
Those are the questions I can think of that I would be asking myself. I feel there is no majic in getting rid of algae, in fact I feel like I have spent more time combating it than I have spent with a clean tank, but I like to feed my fish well and have just decided in my tank algae happens!
Hope this helps a bit, and possibly gives you an idea of something to check that you may not have already.
Good luck!