I don’t have any experience with DWC, as I grow in Coco. I believe your problems are all about PH as you said, and adding supplements to a plant that can’t make use of them thanks to a high pH is a futile exercise. My tap water comes out at a pH of around 8.0 to 8.2 and every single time I mix a new nutrient bucket, I have to add pH down, sometimes a lot, like as much as 2ml in 20l. This is especially the case when I add Silicon which buffers the water in the upper ranges of pH (it is base or alkaline) Plants in Hydro, and especially young plants, prefer a ph of between 5.5 and 5.9 / 6.0. When you get you ph pen you will also notice that ph tends to creep up so you need to adjust the reservoir accordingly. It looks like your plant is suffering from lockout, it’s not getting the nutrients it needs.