Well, newsalt...I'll give ya a bump for now. I've been programmed for reef systems, so I'm not sure what level of nitrates is acceptable in FO or FOWLR systems. I can, however, comment on test kits. If reagents are bad or old, then your results will be bad, if the brand has been known to give poor results, then you'll see -well- poor results. I believe Salifert will be recommended by many as a reliable brand name. Hopefully, others will send some recommendations your way, too.
edit: guess I took too long to post this....so let me add: yeah, what everyone else said! 