I am sorry I am new to the hobby. What is GFO etc. My skimmer is a Berlin 25-250 gallons and my tank is a 120. I don't think I have enough skimming going on because I never dump my overflow cup. Feeding is 3-4 days with pellets and flakes. I very seldom dose. I was just informed that I need to be dosing Iodine for my corals.
so basically you got no skimming going on...
that is part of the problem.
tell me your budget, and I'll suggest the best skimmer for your buck.
also, I would suggest a GFO based phosphate remover, and carbon running in your phosphate reactor, put the GFO in a small bag within the reactor so you can save it, as you should be changing the carbon out every week, but the GFO typically once a month.
as mentioned, what your feeding is important, but if I understand you correctly, if your only feeding once every 4-5 days then your not over feeding, but yes, you should be using rinsed frozen foods instead of dry foods.
detitus removal and physically removing the algae are important as well,
I suggest saving water from your water changes, (fresh decanted tank water, not slimey detritus water) and pulling your live rock out and scrubbing them down in the buckets of tank water, then rinsing them in a bucket of freshly made salt water. if you do this half a tank at a time, and put the corals on the other side of the tank while your doing the other side, the fish can still hide while you do this. pay special attention to sucking up the detritus underneath the rocks as well.
also, running your tank at the higher end of the acceptable ph and alk range will make life difficult for the algae as well. if it is bryopsis your fighting, then elevated mag to 1500 is a good trick too. any elemental changes like that you want to make slowly of course...
you also might want to consider using some live bacteria to boost the colony existing in your system currently, as this will help outcompete the algae as well. prodibio is a good brand to use...
Iodine is a good thing to dose to the system, I suggest getting the lugol's, and simply follow the directions for your size tank. Warner Marine makes a good lugol's iodine. the soft corals and inverts are the ones predominantly benifiting from this, but I would not call it 100% necessary.
using the highest quality elemental additives is super important as well, I would suggest using Elos or Warner Marine brand additives, as they are typically made of pharmaceutical or analytical reagent grade chemicals.
if you did all that your algae would be dying...
ironically enough, my just started tank is showing it's first signs of algae and im pretty happy about it. I will have to put some herbivores in there soon...