[MitchM]

That's a nice looking tank, full of life.

I think there is a detritus buildup happening, between your display tank sandbed and live rock pile.
Between coral secretions, fish excretions and premium food, your tank could be "full". There's no room left for the detritus to go now except for back into the water column.
Excess phosphate will retard coral growth.

I have a few suggestions:
-Turn your frag tank into a 24/7 lit refugium where you could harvest macro algae.
-Use a powerhead to blow out detritus buildup from in behind the rock setup on a regular basis
-vacuum your display tank shallow sandbed on a regular basis (what you can get to, anyways)
-Increase your GFO use.
-Increase your activated carbon use
-Increase water change routine (maybe increase it to 2 X 10%/month)
-Keep harvesting your hair algae. That's essentially what your refugium will be for, except the algae will be kept to the refugium.

The real difficult thing will be the sandbed that is under the rock pile. There is no simple way of cleaning that. That will continually leach out accumulated algae nutrients.
Hopefully you will have some success by running a refugium that can keep up.



Mitch