It's why I haven't messed with hydro in 25 years. Too damned much fiddling around. And too easy to screw up. The only thing I need to pay attention to right now is to let the tap water sit for awhile to let the chlorine perc out of it because I definitely don't want that driving the ph down. Because although I'm rural my water still comes from a treatment plant. That's it. Done and done. And the plants do beautiful. I admire coco noir, but I know I'll probably be messing around with constant testing if I used it. In an end of the world survival scenario novel I'm working on coco-noir is the bomb in the bunker. Compressed like blocks and not taking up space after the apocalypse. The scrap and root bundles can be fed to earthworms which in turn can be fed to chickens.Depends on the media. pH is a tricky thing for a lot of growers, new and seasoned. In soil, pH of input solution is a damn near irrelevant if the soil is built properly. In hydro, you gotta have adequate alkalinity or keeping the solution from swinging like crazy is going to drive you insane.
If pH is diving in hydro, you've bad bacterial cultures blooming. It's a symptom of a deeper problem. pH should be pretty damn stable, on move on a smooth curve as EC and water levels change.
Distilled water could be used, but it's inadvisable since it's zero PPM. Even RO is pretty low but it still tends to have some EC in it, even if it's not terribly significant. You'll just have to use more alkaline buffering and distilled water just isn't economical for long term use.