Ideally, both should be at zero. However, nitrates are generally considered OK if they are less than 5ppm in a reef. Realize, however, just becasue those kits read zero, doesn't mean the algae hasn't absorbed a lot of the stuff. In particular, phosphate kits only measure unbound inorganic phosphates, which may be as little as 2% of the overall picture.
It is a violation of federal law to use this product in a manner inconsistent with its labelling.