What??????
N have the atomic weight of 14. Hydrogen have the atomic weight of 1 Oxygen the weight of 16. The weight of the NH4 molecule is therefore 18 (14+4) and the nitrite molecule will have an atomic weight of 46 It means that the nitrite molecule is around 2.5 times heavier.
If you start with 0.5 mg/l (0.05 g NH4 to 100 L) ammonium and all turn to nitrite - the N content is 14/18 * 0.5 = 0.39 mg/L It normally is expressed as NH4
-N. And in this your right the NH4-
N weight is the same as the NO2-
N weight. The contribution of N to the weight in the whole molecule is the same in both NH4 and NO2. With other words 0.39 mg/L of NH4-
N will be 0.39 mg/L NO2-
N. But we are talking of the weight of the total NO2 molecule and therefore we need to add the weight of the oxygen to the calculation, hence 0.39 mg/L NO2-N is 0.39*46/14 = 0,39*3.29 = 1.28 expressed as NO2. In most - especially older toxicological literature - and in most of our hobby tests - the concentration is expressed as the whole molecule - in this case NO2. In environmental and when a mass balance is important - it is normal to express the concentration as nitrogen nitrite (NO2-
N) In our case - toxicological considerations - we are interested of the whole molecule (it is that which is the important and toxic - not the N or O - just the combination. Compare NH4 and NH3 there is should in a toxicological point of view be total meaningless to use NH3-N as the measurement. Most litterature and testset use NO2 as nomenclature. There is some that use NO2-N and it create a lot of misunderstandings.
I will take an example. We start with a 100 L aquarium (if you want to understand the basics of this - you need to use the metric system) 100 L is around 26.42 gallon. The instruction says that we should start with 1 mg/L (nearly the same as ppm) ammonia (I use NH4 as example here) This means that I need to add 0.1 g of NH4 into the 100 L. Thats means when ammonia reads 0 - around 0.1*14/18 = 0.77 N has be transferred to nitrite - the NO2
- N is 0.77 But the NO2 is 3.29*0.77 = 2.5 mg/L NO2 (ppm NO2). Now - the process stall - as it could and the aquarist that follow instructions add another 1 ppm ammonia on day 3 - because the second step is stalled 2.5 mg/L of NO2 will add to the other 2.5 and you are up in 5 mg/L of NO2.
I have seen advises here to start with 4 ppm ammonia, following up with more and confirm the first step with more addition of ammonia. All of this without measuring NO2. In worst case if you to a 100 l aquarium have started with 4 ppm ammonia (0.4 g of ammonia to 100 L). adding another 0.4 g at day three and control the first step with another
0.4 g - the total amount will be 1.2 g ammonia or 1.2*14/18 = 0.93 g NH4-
N to the aquarium an in
worst case it will be 0.93 g of NO2-
N in 100 L -> 9,3 mg/L NO2-
N. 9.3 mg/L NO2-N is 3,29*9,3 =
30.6 mg/L (ppm) NO2. This is in worst case with a stalled second step - which means no or very small amount of NO2 converted to NO3. and this is a very common scenario when you start a nitrification cycle with high addition of ammonia - IMO
To this I can add that we are in a pH around 8 - 8.5 and some free ammonia will be formed (NH3) Free ammonia itself have been shown to suppress the second step at least in freshwater but in higher concentrations that we normal have. However - with the methods to add ammonia in saltwater aquariums start up - I have seen tons of reports that indicate stalled nitrification cycling process, And with stalled I mean that the second step NO2-NO3 not working properly.
I hope this will clarify why I have the standpoint I have. Nitrite measurements is the key factor in order to know if the whole nitrification cycle is working in a proper way or not. IMO if possible - no living creatures should be added before it is completed and seamless and 0.1 ppm NO2 is a good threshold. However there is methods to start with low amounts of daily contribution of ammonia -
like my 15 steps - (an slow rising of the amount) and/or adding biofilm or/and photosynthetic organisms early in the start up that hinder the stall of the cycle and that you never will see a nitrite peak,
Sincerely Lasse