No matter how much PH down is added, my water natu...

So your PH keep getting high because you did not buffered the clay balls (hydroton) at the right PH before you start your grow. Clay balls are rarely pre buffered so each time you plan to use them save a week to buffer them properly. Now that you are in you can't go back so continue to give some PH down , it will slowly buffer the clay balls until you reached a PH that did not fluctuate like that. An other possibility would be your fertilizer: maybe it is a formula that lead to PH fluctuation. Your leaves could be affected by the PH but also by your very low RH : 30% is for the last week of flowering 😊✌️🏼