As ever, I'm appreciative of the information you've shared on this and many other threads, DS!
I run a homebuilt UC style RDWC system. Recently, I figured out that drowning the buckets was bad juju, lol. I'm still learning a lot about the system and the dos and don'ts.
For a nutrient package, I use Jacks Professional Hydroponic 5-12-26 and 'generic' lab grade Calcium Nitrate, with a little bump of epsom salts, aka magnesium sulfate. As an aside, I'd love it if you could work your nutrient analysis magic with a bit of Jacks, so I can make more informed decisions about usage rates!
This stuff apparently doesn't have much buffering agent in it, as it likes to shoot up (even as far as 7.5!) when I first put it into the system. I end up adding several doses of GH pH down powder over the course of several days until it stabilizes. This represents the upper part of my 'swing'. When I get the pH under control, it generally ends up in the 5.5 to 5.8 range, where it slowly drifts up again over the course of a couple of weeks. Then I change water, and start all over again.
So far, so good. Between this and chilling my water to 64-66, my pathogen problems are at an end, my girls look vibrantly healthy and they're growing like crazy, far better than with anything I ever got from a 'hydro store'. Nevermind the fact that I'm saving a bloomin' fortune on nutrients.