The sensitive ones may not live long.... in the sea, there is almost zero nitrates, unless u are close to shore, mud flats, mangrove areas, dirtier lagoons.
Nitrate is a form of nutrient which the zooxanthellae in corals will utilise to some extent, causing an overgrowth, thus making corals brown.
To keep SPS colourful.... try to replicate almost perfect water quality.