Step back and look at your system. Do you have a denitrating source? The stuff is not like junk in your basement where you bring in extra crap until it is full and then it stays there. The rock and sand will constantly turn it into nitrogen gas when it is stable and ready to go... you will constatnly fight this and the more nitrate that you add, the more anoxic bacteria will grow to consume it. You need to consider the living, breathing ecosystem that will adapt and modify - this is not a static math equation.
Instead of adding nitrate, just feed the fish more. Most corals prefer to get their nitrogen from ammonia and ammonium and not from nitrogen which requires more energy to get the nitrogen from the molecule. Unless you are wanting to poison dinos or diatoms, then ammonia/ammonium is the way to go for corals.
Seriously, if your tank is less than a year old and your corals are still frags, then they just need more time. Nobody has good looking corals in a young tank without putting a lot of makeup on them with RB LEDs.