it has been set up almost a year,,, just moved to Florida,, no I never had a problem with cyanobacteria and or Nitrate problems? I only keep 4 small fish and a few dwarf seahorse in the refugium, fish cause problems ,,,
try increase your flow ,, flow is very very important if you cant see your water and animals moving around you don't have enough water movement
I have 3000 in a 120
cyanobacteria will not do well with high water movement also make sure your making your own R.O-D.I water and not buying it from your pet store. They never change filters enough
for nitrate how long has tank been running I have a feeling you have to many fish or have lost to many fish in the tank
make sure you have a brittle star to make sure dead things get eaten
hope this helps