I have make something for you.

Its not compleet and not exact, but a step in the way you want (i think)

Good luck

Nice work and calculation

But some seem not correct, I not use the AQ1 analog out, but the digital out Q16.

I try to delete your AQ1 and insert the Q16, but cables are not compatible, can you fix?

The Q16 turn ON the Valve to load the KOH on tank when the KOH concentration is missing ( less 25/30%)

Thank you again

Use a analog tresholt block

Connect the input to the analog value and connect te output to the digital output.

Make EN (Enable) High