It may be that who ever is letting it sit is also aerating it. (Would that
dissipate some of the ammonia?)
There has a been a round of threads on the killie lists about mystery deaths
in several tanks after water changes with municipal water. Wright Huntley,
has especially rung the alarm on a couple of lists about the danger of just
using sodium thiosulphate which frees up the ammonia in the tap water. He
had been pitching using Amolock or Amquel.
Wright responded to one person who had experienced sudden post water change
die offs in several tanks with ...
*Have you checked your water for free ammonium? That's common in water in
some agricultural areas, and is readily cured with aeration. It takes way
less than 1 ppm to cause permanent damage in some fish. I know from sad
experience that some Nothos are really intolerant of even low
ammonium/ammonia levels.*
One of the ironies of that treatment is that evidentially Amquel's active
ingredient is something like formulin. Several of us who feed daphnia saw
mystery dies offs after use of the Amquel treated water. I guess you have to
keep the water in the light and then aerate it a couple days more.
With the temperature well below freezing for going on two weeks now around
here, it is hard finding a nice sunny location outdoors to season our water.
If you love keeping fish, you do what you've got to do.
All the best,
Scott