Thanks Hq. So does toxicity/salt build up start showing itself on the bottom of the plant and work it's way up? The only signs I'm seeing on the top of the plant are some very lightly yellowed leaf tips, as if they've been ever-so-slightly nute burned. But the damage on the bottom is much more ravenous, and has a different look. As shown in the images, it's sort of like a cripsing of the leaf from the outside in.
Depending what is locked out macro or micro nutrients signs will show on top or bottom. If your ppm raises in your run off you are feeding them too much. Run off ppm will drop if plants are hungry. I see you are running canna coco plus calmag. Canna coco is buffered with extra calcium for the extra needs of coco. My guess is you have filled the calcium buffer and now have excess causing a toxicity problem.