Chloramine, that's what killed my fish. I have been told my local water company puts Chloramine in the water every time they charge the system. Chloramine is a combination of Chlorine and Ammonia. It is commonly used to treat municipal water in many areas. That is why my tap water tested .50 for Ammonia.
There are products available to remove Chloramine from the water, I just forgot to use it on my last water change.
I am sure there are test strips also available to test for this chemical.
Be aware, if you use municipal water, Chloramine is probably in your water and it is deadly to fish!

