Just my .02 as a hydro noob myself.
Over water = lack of oxygen. I chose to not use a bucket system because there is always some water left behind in bucket. Could be that the roots are using up all the oxygen in that water between watering making it look like it's a over watering problem when it could just be a lack of oxygen. May need to water more often to keep the bottom of the bucket oxygenated?
Do your RW cubes get wet during the water cycle? If so, then it could be compounding the problem of actually over watering and lack of oxygen. I keep the RW cubes around 3/8 - 1/2" above top water line to keep the cubes dry.
Toxic levels of nutes, or nutrient lockout? 6.0 is a bit high PH for hydro. It won't allow some stuff that the plant can get with a lower PH. One problem I'm having is snot algae in my rez'. At first I panicked, and did everything to get rid of it. Since then I've come to terms with it, and I think it may actually be benefiting me to some extent. It gets the PH rising after a couple days after my H2o2 dose. So I set the PH below 5.8, to around 5.5-5.6 and let it drift up to 6.0 before adding PH Down. This way the plants on day 1 get more nutes that it can absorb with a more acidic ph, and by day 3 or 4 they are easily getting nutes it can take readily closer to a neutral PH. Maybe try fluctuating your PH up and down to see if a nutrient lockout is happening. Or just set it at 5.6 for a few days, then raise it to 5.8.
Man, I can't even get threw the list of stuff you're using for nutes. Looks like a lot of work measuring it all up. I'm using Canna because I know the manufacturer does a good job of putting everything it it for me. Everything the plant needs is in it, so if I get what looks like a deficiency, I kook elsewhere [like PH and lockout] knowing that all the stuff is in the mix I buy. Less of a chance I can fuct it up. Maybe try changing nutes for a while and see if it clears up?
Good luck! It's a real bummer to see plants having problems, especially after doing so much work to try and keep them happy and healthy.