I've always been one to shoot for "natural" levels, but for years I ignored my phosphate and nitrate because I didn't have an algae problem and my corals were colorful, but now I'm in my own personal competition to get photos of yellow, pink, and red corals that are as colorful as Kryzstof Tryc so that means maintaining an Ultra Low Nutrient level. At the moment I am testing with a:
Hanna HI736
and the
Red Sea Pro Nitrate kit
but I ordered the
Hach NI-14
On the Hanna Phosphorus checker I shoot for 1-2 ppb. I got to that number by reversing the NSW level of 0.005 ppm phosphate
(0.005 x 1000)/3.0661 = 1.6 ppm phosphorus
and on the Nitrate kits I essentially strive for zero since NSW is 0.1 ppm and the test kits only have resolution of 0.2
Interestingly enough I find that my phosphorus will vary from 0 to 10 ppb but I can increase my NOPOX to about 30 ml max in a day and it will knock it back to 1 to 2 within 24 hours.
Since I started this new regimen I'm also dosing Salifert Amino Acids and Brightwells ReefSnow and Brightwells Zooplankton plus I'm testing for Potassium now and trying to keep the levels slightly above 400 ppm.
All that to try and grow corals as colorful as Kryzstof . . . I know . . . I must be nuts

Funny thing is so far so good and all my corals seem to be doing fantastically well at the moment.