water parameters

1. At what ph does ammonia turn into ammonium? 2. If there’s a fish that needs ph at 6.5 or higher then can it live in ph of 7.0 that lowers to 6.0 with co2? Or does the ph change from co2 not affect it like that? I know co2 doesn’t affect kh.

is a ph less than 7.0 too low for least kilifish? I’m getting netlea aquasoil and it lowers the ph a lot. Sometimes down to 5.0 I’ve heard, but I’ll be doing weekly water changes so it shouldn’t lower that much, but still under 7 for sure. if least killifish wouldn’t do well in that then I...

Yesterday was a very bad day for me and for my fish, one of my tanks is a community tank with different species, it was the weekly maintenance day where I do tanks' maintenance and change 50% of the water and of course use a de-chlorinator to remove any tap water chlorine; I have been doing this...