420puff,
Don't give up, man. I had the exact thing you did (search out my nightmare here on RDO). At the time my tank was about 4 months old. I got an aweful outbreak of brown/green snot dinos. Here is what I did and it took over a month to clear it up:
All my params were excellent and no Phospates could be measured
Siphon out all snot strings every day
Ran my skimmer 24/7
Stopped all additives (like DTs Phytoplankton)
I did 20% water changes daily with 0 TDS RO/DI and IO
Dark for 2 days at a time and then 4 hour light days then back to dark
Drip kalk to raise Ph to 8.6 (monitor this closely)
Added PhosBan just in case
Ran
TLF carbon and changed it twice a week
Fed my fish about 1% of normal diet and used NO Frozen/Meaty foods
Removed EVERYTHING that didn't need to be in the tank (dead snails, etc)
It finally went away but it was the hardest thing I ever battled with my tank. Don't give up!
Good luck.