injection regulation #29

Hi,
I'm building your project but I have some questions:
My configuration is ESP8266 to manage all system with ( PH + ORP ) sensors + 2 relays for injections ( motor control+temperature I've already contected it before ), I use Home assistant to manage whole house and for the swimming pool I do it as well.

I don't really understand how do you manage the injection, As I can see is it possible you do it manually from user panel?
If it is automatic, I don't really understand how to mesure injection time depending on ml/min peristaltic pump , concentration of bleach or muriatic and measures you take form probes... but maybe I'm wrong. I will thank you if you can explain it a little bit, in my case I should increase PH so I should inject PH+.
Thanks