Well there's a little more to it than just the colors.
No3 promotes zooxanthellae on corals which gives you in return the colors, in a low nutrient system ppl will see pale colors if proper dossed with for example the KZ products zeo you will see the famous pastel colors.
Hobbyist have to be careful with dosing No3 as you can dose to much in short time a trigger a algae war.
Some algae is good in the reef tank as no algae is never a reeftank, with no algae your Po4 will go like a JoJo.
Now algae can mean a lot, if you can't spot algae on your rock than IMO you are of balance.
Hobbyist brag a lot like I clean my glass only once a week, what does that tell you?
That's why it's important now days to test for No3 everyday as it is one of the important nutrients in your water.
Potassium, yes promotes the blue/purple colors but also growth, K needs to be around 390 give and take.
With a ULNS you deplete K super fast as it can drop to a low in week time from 390 to below 300.
For that is No3 important to keep that ad balance.
Iron is something else ppl think you should dose it but our salt mixes have a high level of salt already, NSW level is at 0.0034.
Some ppl will maintain it at 0.15 but my question is how could they test for that?
0.15 ppm is so ridiculously incorrect it's not even funny.
Iron is measured in the parts per trillion range in surface seawater.
There is really no point in trying to test it with hobby test kits.
It is far too low in concentration to be detected without super fancy tools.
Triton test will come good but often gives a false reading and that all depends on having macro's or not.
With regular WC you will balance out the iron but also the Iodine.
If you go the route as many other all ready have done, you be forced to do a monthly Triton test as it will tell you the elements that we by our self can't test for.
That's a other conclusion but not relevant to this topic.
