Like being said above Zero nitrates are not good.
Managing your nitrates in relation to your phosphates is the best option. The ideal Nitrogen to Phosphorus ratio is 16 to 1.
This means if you want a Phosphate of less then .02ppm (.004ppm Phosphorus) you will need a nitrogen level of around .06ppm or .3ppm nitrate.
Zeros across the board do not result in colourful corals. You colours will be washed out. Check my recent post on my 73 gallon tank.
The top growers of corals for resale are maintain their nitrates in the neighbourhood of 5ppm or higher. Check on the web in regards to companies like Battle Corals or aquariumcreationsonline.net.
Please read the following article: [url="http://wateralchemy.blogspot.ca/2012/03/nutrient-reduction-using-organic-carbon.html?m=1"]