Tatu & Company
This will be along post so bear with me
I agree on your choice of kits if one wants to get picky.
Before we go anywhere we all need to be on the same page. The best example is: " my Nitrate is 1 ppm, well my nitrate is 5 ppm". Ok, they both have the same reading . One kit is expressing it as NO3-N and the other as NO3- (ion). The stds in the water world are expressed ad "N" = Nitrogen. It has been becoming practice in this hobby to use NO3 (ion). Half of the kits in this hobby are in each but there is a trend towards the NO3-(ion). I have never like the N expression. This is not the same for ammonia and ammonia gets even worse.
What is an expression in chemistry. Well, it is not the same often like it is when comparing them to inches to centimeters or F to C. Actually you can express something anyway you want. I do not have to express Ca++ as that. I can express it as CaCO3 which is very misleading. I can also express, if I choose, as lead, gold or what ever I want. It is just a weight thing. Obviously we do not want to do the latter.
First, almost all ammonia test kits measure TAN= Total Ammonia. There are a couple out there that actually test for NH3-N. One can only assume the test kits that say NH3-N, are actually TAN. If it explicitly says NH3 or if the kit says it tests for TAN and NH3 then we can assume that is what it is doing.. This means that even though the kit expresses it as NH3-N or even NH4+ - N, it is actually measuring both.
Second, Some kits in this hobby express it as TAN or TAN-N more confusion. I wish these kit manufacture would get their head out of their butt
Most kits no matter how they are expressed are actually TAN or TAN-N.
So what is all this in the numbers game. The conversion is 1.2 or 1 ppm TAN -N= 1.2 TAN. Almost all sources we read in this hobby by far are expressed in real terms as TAN-N. i.e., fish toxicity, invert toxicity, etc.
As pH rises the ammonia gets converted from NH4+ to NH3, as at higher pH there is less H+ in the water. At SSTP-NSW parameters 90% is NH4+ -N and 10% is NH3-N. The most dangerous/toxic of the two by far is NH3. The real killer. Since the two are a function of pH and temp it really makes no difference what the kit actually tests for. It is just a math calculation, kinda like ppm Alk to Meq / l or dkH only more complicated. But we do need to know if it is an "N" kit.
For most fish and many inverts this level is 1 ppm TAN-N or a calculated 0.1 actual NH3-N. Many of the kits in this hobby only go to 1 ppm i.e., 0 -.1 -.2 -.3.-4 .-5. -6. -.7-.8 -.9- 1.0. Most fish at this 1 ppm TAN-N will die in 3-5 day if there is not immediate action taken. You need to know what your kit is expressed at. For example; IIRC the Salifert is as TAN and not TAN-N. Someone check for me
These two links will explain all about ammonia, allot is repeated. The first link has a calculator if you wish to know how much NH4+-N you have vs. NH3-N. The other link has a table.
As TAN-N
http://bridge.ecn.purdue.edu/~piwc/w3-research/free-ammonia/nh3.html
As TAN
http://edis.ifas.ufl.edu/BODY_FA031#FIGURE 3