Fish dye after water change

[Love_MyFish]

Can anyone tell me why almost everytime I do a pwc I seem to find a fish a day or,two later dead? I do pwn with an aqueon water changer and I dose the whole tank with prime. Seems to only happen with the tank I did the fish in cycle. Are they just dying off due to being hurt during the cycle? The tank has been set up 8 months : ph-6.4 am-0 nI-0 nA-10

 

[Homedog98]

What are the water parameters straight out of the tap compared to the tank water parameters?

 

[Love_MyFish]

What are the water parameters straight out of the tap compared to the tank water parameters?

Ph same am .25 ni same na same