are you skimming? how often are you doing water changes?

both will reduce your nitrates significantly

as far as the cyano and urchin go, grats. i had an urchin that wouldnt touch the stuff. i was cool with him as long as he ate the coralline near his burrow (i had a rock burrowing one) but when i caught him munching down on the coraline on my back glass, he was caught and gone within minutes. in just a few hours he had went through the greater majority of it.