"Granular ferric oxide...you put in a reactor or bag in high flow area and it reduces nitrates"
Almost -:angel: it does nothing to nitrates - it removes phosphates.
Its not very expensive - check out Bulk reef supply. It gets a little expensive if you buy the phosphate reactor etc. You can put a little in a mesh bag and drop it in your sump or canister filter or other area of high flow. Me - I usually just put a small scoop in a bag in my filter sock. It will take your phosphates down.
Spihon what you can - without destroying your tank - take a power-head and blow off the "unsightly" stuff you can't suck out. A toothbrush helps in small spaces. Its not a big deal - you just want to get out as much as you can. If it comes back slower - your winning.
If you don't appear to be making progress - or your in a hurry - chemi-clean would work.
Will this be a fish only tank - or are you planning on corals too?
I first plan on adding a frogspawn or an anemone and a pair of ocellaris clownfish. After I add these, I want to try and add a few corals. Im debating whether I would rather do LPS or SPS.
Honestly, I think I will go with SPS because they are more hardy than LPS .
@Pappy - I knew what you meant :wink: - I mistype all the time.
@Saltwatertaylor - The reason I ask is with fish only you don't have to worry with nitrates much - LPS/nems also are not too sensitive to reasonable levels - SPS generally need it cleaner for good color.
I also run a 120 (115 really) - LPS dominated with several nems. It sounds like your almost there - this cyano thing in new tanks is really common.