IMO feeding too much. Nitrogen toxicity. Causing other nute deficiencies. Too much Nitrogen can also acidify the soil. Making it sodic, poorly draining. Dolomite lime corrects all those issues.
Ehhh not really. Excess Iron and lack of P+ will make dark/blue green. The clawing leaves and fried leaf with huge necrosis from nitrogen burn are my tip offs.
I gotta be honest that I don't know what it is as many signs as it's showing, but everytime I've had a nitrogen toxicity problem personally my leaves have been really dark green and hooked like talons into points by the be time it got bad. They look pretty pale in comparison. What EC/PPM have you been feeding them? Do you feed them to run off a little bit each time? Also what temp is the environment in?
Every single post that has dying plants has one thing in common..."I'm giving nutes + cal mag". I'm in Coco and NEVER once used cal mag. It's the most overused nutrient period. Every issue is not "calmag"