Couple of things bothering me when I look at your pics.
1. Your hydroton (clay pellets). Did you clean and check the ph on them before you used them? Because they look dirty to me. They tend to absorb minerals over time and cause massive ph swings up. I think this is especially true when they dry out. Which brings me to:
2. Your coco is dry. It's damn near impossible to over water coco. When coco dries out, BAD THINGS HAPPEN. Dry coco has a crap cation exchange capacity and is full of salts which locks out beneficals like calmag and iron and again screws up your ph. It's a lot easier to deal with when you start in smaller pots and then transplant into bigger as they grow. You need to keep the all the media in your pot wet and fertigate multiple times a day.
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