CANNA cal mag (buffer) their bagged coco prior to sale wordtree so stop with the cal mag. They're showing what looks like an N deficiency (N is highly mobile and its deficiency shows in new growth) so hit them with a foliar spray to compensate for now and they should come good. Perhaps raise the lights to gently help them along also.
I think your on to something bro. It didn't occur to me raise the PH to reduce the uptake efficiency.Let your Ph drift to just above 6, cal, mg and P all are a lot More available when you are hovering around 6.
Best advice I found in this thread,
...
I'm tempted to say N def or lockout, that's what it looks like to me, but it could be something else. Have you been giving them the full feed (4ml A+ 4ml B/l) or do you cut doses?
under what conditions does N lock out?
I'm a coco grower and keep my pH 5.8-6.2+.
edit: Retro^^, must be a hydro guy to recommend a pH range of 5.5 to 5.8. I'd never go that low in coco. To much risk for cal and mag defs.