IME this is how you beat HA
*Start with a good 25% water change and then follow up with increased water changes (10%) every 2 -3 days for 2 weeks. then dial it back to twice a week and then once a week. vaccum the sand, pick the rocks, blow em off too.
*get a GOOD cleanup crew. plenty of Trochus snails, scarlet hermits, margarita turbos, nerite snails, nassarius snails.
*reduce feedings and strain the food well through a mesh net.
This method will slowly reduce your nutrients and not shock the corals *(which have probably become accustom to higher nutrients) and the CUC will eat the rest. You will lose a few snail and hermits along the way but in teh end you'll have a clean tank.
Be diligent and patient and you will beat it. Especially with a medium size tank like the 75, the water changes and CUC will take this down within a month. Adding GFO can create its own problems by stripping the water too quickly of the nutrients and thus stressing corals.