There's a table floating around on this board somewhere that shows which nutes are absorbed at what pH. (It's different.)

You WANT some drift. High 6's is a bit out of the sweet spot but in my experience, no big deal unless you leave it there.

I had some pH swings in a coco test I did until I added the plants into the experiment. Then everything leveled out.

But if you can knock the pH down to a number you like, and it slowly and predictably swings back up through all the nutrient uptake ranges, that's just about ideal, IMO.
DreadedHermie Reviewed by DreadedHermie on . RO H20 + Cal Mag Plus = Unstable pH Hello farmers having some pH problems. Here's the setup... 20 gallon tote with 6 airstones for a bubbling DWC for seedlings. Inside the 20 gallon tote there is currently 15 gallons RO H20 w/ 75 mL of Cal Mag Plus (5 mL per gallon Cal Mag Plus). There is nothing else in this reservoir. Air temps are around 68 degrees farenheit and water temps are between 63 - 68 degrees farenheit. Rating: 5