I agree with everything
@Richard Drysift said with one exception, I run my PH closer to 6 than 6.5. if you’re 5.8 to 6 you’d be golden in my setup. I’m a hydro grower, but never done an ebb and flow, so it might be a bit different. In a water grow a ph over 6 can lock out iron, but it depends on how the iron is chealated. I run over 6 a bit sometimes but my plants are happy there so the iron in my fert appears to be well chelated. In my setup if I run it 6.5 or 5.5 the plants can pull up too much ppm too fast and they burn their tips the next day. It depends on the fert though.
You can definitely save them. Can you raise your humidity? 50 is great in flower but it’s low in veg especially for plants that don’t have a lot of fluid reserves. You’ve got to be sucking those plants dry with that low a humidity and just a rock wool cube with some hydro clay around it for reserves. You’ve got to get them on a regular fluid schedule. I’d help with that, but I’m not an ebb and flow grower. Lots on here. Try a search for it and pick up some tips. At the least dip them in the solution more often.
You bought a Bluelab PH controller? That’s a serious investment; how large is your holding tank? Shit, I’m jealous….
I read that they only adjust the ph one way. So you set them up to dose up or down, not both. Is that true?