With all due respect to my seniors, I don't think that it's quite that simplistic, Duane.
I have been recommending bulk sodium thiosulfate for many years, but only to those on chlorine systems, not chloramine. I think that with chloramine there are too many variables that allow for mistakes to happen.
For those that don't understand the basics - when chloramine tap water is treated with products such as Prime, Safe, the chlorine/ammonia bond is broken, resulting in a certain amount of free ammonia (NH3) that needs to be bound or reduced into a safe nontoxic form. The toxicity of free ammonia is highly dependent on both temperature, and pH, so this can vary GREATLY from one hobbyists tank to another.
A good read on the toxicity of ammonia and fish can be found in the following article posted on the krib, and consider that some researchers now feel that some of the EPA values stated in the past may be underrated, or undervalued.
http://www.thekrib.com/Chemistry/ammonia-toxicity.html
Experiments have shown that the lethal concentration of free ammonia for a variety of fish species ranges from 0.2 to 2.0 ppm.
Experiments have shown that exposure to un-ionized ammonia concentrations as low as 0.002 ppm for six weeks causes hyperplasia of gill lining in salmon fingerlings and may lead to bacterial gill disease. At higher levels (>0.1 ppm NH3) even relatively short exposures can lead to skin, eye, and gill damage in some species.
Obviously free ammonia (NH3 ) is toxic to fish. How long that toxin will remain in one’s tank, and how toxic it will be, will be dependent on a number of factors. Temperature of water, pH value of water, planted tank vs non-planted, size of biological filtration, whether the biological filters are well established, or not, size/volume of water change, duration (time) of water change, species of fish, life stage of fish, level of chloramine in system, and last but not least, frequency of exposure. Did I miss any? There are a LOT of variables involved!
Even if one tests after the water change, as Duane described, and comes up with a 0.0 reading, there may still be low levels present during the water change. Some of my refills are over an hour in duration - and I know from experience that there will be free ammonia residual during the refill, unless I use a product such as Prime or Safe. And this is with a massive amount of very active & well established bio media in place. Bio media can only work so fast. I can't even imagine what faces those that have uber high levels of chloramine during certain times of the year, such as heavy rain periods, spring run off, etc.
“A single or simple concentration measurement of ammonia is not sufficient to evaluate and/or regulate ammonia contamination. The influence on the toxicity of ammonia to fish is impacted by both duration and frequency of exposure.”
http://www.nature.org/images/ammonia-literature-review-dec-2010.pdf
With the value of dry powder formulas such as Seachem Safe, and all the various unknowns regarding safe levels in different species of fish, and their age groups, I see no reason why anyone on a chloramine treated system would choose to not use a product that would not only render the chlorine portion of chloramine (chlorine/ammonia) safe, but also render the free ammonia portion to a fish safe form. IMO exposure to low levels of free ammonia from external sources are very much along the same line as second hand smoke, something that my generation ignored for several decades.