What is your pH? I'll bet it is under 7
With a pH under 7, there is almost no ammonia (NH3) in the water, it's all ammonium (NH4+).
NH3 is toxic to fish but not NH4+.
If you want to raise your pH, you must first make sure you you get rid of all this ammonium, or as your pH raise it will turn into NH3 and kill your fish.