I think you've run up against the big question that arises when more than one plant shares a reservoir. If they need to be treated differently, how do you do it? You can't. So you need to pick one middle-of-the-road feeding approach that doesn't burn any of them…and then live with any deficiencies one or two might have (though I think if you do a max 800 ppm program you should be fine).
Yes, even plants of the same strain can have different needs, but they're probably going to be closer than plants of different strains. If you have trouble this run because the strains are different, then maybe modify your equipment next time so that half your buckets are running off the same res and the other four are hand-filled individually or hooked up to a second res…and then run two strains.
Good luck!