If you have Cyano in a fuge but not your main tank, why is this a problem? I personally accept that some cyano blooms are inevitible. As long as they "choose" to bloom in the fuge vs. the display tank, that's just great. Now I also recall you said you had cyano on your macroalgae. If that is interfering with growth of the macro, that's bad. Otherwise, again, why is it bad?
I have a very new tank (~6 weeks old) with a lot of very healthy live rock. There is some nitrogen processing going on in the sand bed (bubbles visible about 1/2" - 3/4" from the top at the side of the tank). My test kit (FWIW) reads zero nitrates and somewhere between 0 and .03 ppm phosphate. I am using RowaPHOS though and I have a very light fish load and don't feed much.
After reading this thread, I'm tempted to remove the RowaPHOS to see if it helps my Macro grow. The Caulerpa is growing fairly well thought, so any change would violate the "if it ain't broke don't fix it" paradigm.