Something's screwed if you're getting a big fluctuation of pH in one day. Most people fret more than needed over pH and a swing back and forth is good for the plants. 400 times/day sounds like you are one of those people.
Switch nutes to AN pH Perfect nutes and stop worrying about pH.
I've done DWC for almost 20 years and even before pH Perfect I would set my pH around 5.5 and it would climb to 6.2 over the 3 days between top-ups then I would add a few drops of conc. sulphuric acid to the tub without checking pH once I got used to the rhythm of it. Just check ppm and a dash of nutes to bump it back up to my target.