Overwatered cubes in hydro? Too close to the sun? or effect of having add

I don't think it's overwatering, it's because your rockwool blocks don't contain any nutrients to begin with, try next time soaking the blocks in water with fertiliser for a few hours beforehand. I had exactly the same problem.

@Maddiq yes they were too wet to start with but that is a pretty healthy root hanging down into the nutrient solution so your plant should recover fine . from now on try to keep the rockwool cube and zone around the plants trunk relatively dry so that you don't run the risk of rot developing there Good luck mate 👍

I replied to your other post, but sounds like overwater for sure. I’ve had this happen once before using the cubes and it was because they were absolutely soaked. Hope this helps.