Ok this answers why the PH stays so high even after passing through the RO.
www.freedrinkingwater.com
If PH is the only reason to run the RO then don't. Just use your tapwater treated for chloramines. I have learned something new here and I apologize if we took a wrong turn. I falsly believed RO water was always 7 PH - Wrong.
Ok that part does not change the need to keep the PH in the root zone in tolerance. The strategy here will change in coco.
Remind me how much PH down you use on just your tap water?