i don't believe we get accurate nitrate readings due to many factors. i also don't believe your nitrate readings need to be zero in order to have happy corals, including sps
i maintain a tank at the "devon fitness club", which i have free reign to do what ever i want to. i don't check nitrate levels, but i do water changes.
weekly, the water coming out of that tank is yellow.
meanwhile, i have recently added a piece of acropora, and it's coloring up and growing nicely, with full polyp extension.
what do you think the nitrates are in that tank?
i'm betting higher than most of your tanks.