There are no miracles or mysteries, nitrate level is a function of what and how much you put in and how efficient is your mechanical and biological filtration system.
Good skimmer should remove lots of organic matter, quality live rock should complement it thanks to nitrifying and denitrifying bacteria.
It takes longer for denitrifying bacteria to get established in a reef tank and sometimes you can achieve maturity many months after establishing system.
As for dosing carbon (which nopox is), it should eventually work, you either are below optimal dose or you are not eliminating nutrients by effective skimming.