"SA" wrote in
:

[Snip]
I too was not certain as to whether or not it was ok to use the
python to fill the tank as opposed to a bucket of water that
gets prepared first. But I figured many people use their python
to fill their tanks and I have in the past also without an
incident. I wasn't sure if adding the water treatment was
supposed to be before adding new water or during, I figured
during would be better.

[snip]

Steve,

In my experience, after reaching a certain threshold concentration,
chloramine, a chlorine derivative common in many public water
supplies, is instantly toxic to fish. Something in your post
suggested to me that you might have added dechlorinator (most such
products also neutralize chloramine) several minutes after
completing your water change -- a water change that was more than
usual. If that had happened, then there was a chance that you had
poisoned your fish with chloramine. (Smaller water changes might
not be enough to reach the toxic threshold, so you may never have
noticed this before). I know this can happen because I did it once,
when I was young and ignorant, to a tankful of Tanganyikans.
However, if you were adding dechlorinator at the same time as adding
water, then I would not think chloramine would be the explanation.

Regards,
Meph