fish dying (long Post)

[MitchM]

I think you're on the right track.
I'm pretty sure that Calgary doesn't use chloramine, their water report only mentions chlorine.
Even if they did use chloramine, the Prime would bind the ammonia.
Lowering the temp is a good idea.
I wouldn't try to force the PH down.
Larger water changes would be better, but you can only do what you can do.
I don't know if adding more Prime to the main tank would immediately lower the ammonia, but it sounds like it's worth looking into.