Tank often go through an algea/cyano stage in the first yr.
Crank up the flow up,
Blow off the rock with a PH before water changes
water change to 25% weekly
make sure your skimmer is in good working order
siphon off any detritus
reduce feeding
....rinse and repeat.
Also check you top off water and salt mix water TDS and make sure it is Zero, if you are not using RO or RODI start using it
GFO should be a last resort and only used to put things back in order. If you can not manage your nutrient levels without it you are doing something wrong