Nitrite and nitrate - ions or compounds?

map2022 · Feb 15, 2022

I'm in the middle of cycling my first saltwater aquarium and, like any good newbie, I've been using my nifty API Saltwater Master Test Kit to check my tank's ppm NO2- and NO3- each day. But this morning I had a flashback to college chemistry and realized my tank probably isn't full of free, negatively-charged nitrite and nitrate ions. (Or maybe it is?)

So I'm curious.

In what form do nitrites and nitrates exist in aquarium water? Free ions? Salts like NaNO2 or KNO3? Organic compounds? All of the above?

How do hobbyist test kits for nitrite and nitrate typically work? What am I really measuring when I test for NO2- and NO3-?

(And what I really want to know right now: could that last bit of stubbornly-persistent nitrite be in a different form than the rest? Perhaps a complex organic compound that my new tank isn't able to break down yet?)

Thanks a million for any insight and for indulging this chemistry dilettante!

Spare time · Feb 15, 2022

Nitrate in the Reef Aquarium - REEFEDITION

Nitrate is an ion that has long dogged aquarists. It is typically formed in aquaria through the digestion of foods, and in many aquaria it builds up and can be difficult to keep at natural levels. In the past, many aquarists performed water changes with nitrate reduction as one of the primary...

www.reefedition.com

http://reefkeeping.com/issues/2005-06/rhf/index.php

These might be of help

Randy Holmes-Farley · Feb 15, 2022

All ions in seawater exist as individual ions surrounded by water molecules, some of which are tightly bound, and then surrounded by other ions with an excess of the opposite charged ions nearby by.

Nitrate is a negatively charged ion, NO3–. It consists of a central nitrogen atom and three oxygen atoms attached to it. The negative charge is spread out equally over the three oxygen atoms, making them all identical. It is generally very soluble in seawater.

This artivle of mine has a very detailed descriptiona nd pictures of what that hydration sphere of water molecules means, in this case for calcium ion: