Master Kush Sick yellow leafs lime green and dying.

Master Kush feed with Canna A&B alternated with H2o PH at 6.3 as needed. All have little brow spots on them. Just this one Sying. Please Help.

Is it in a container or in the ground?

Calcium lockout probably, maybe phospohrous (i dont remember which one does weird spotting necrosis spots). Yeah is it in a container or the ground? If it's in a container, flush some water through and check the TDS of the runoff water and see if it's more than a couple hundred ppm higher than the water going in. If it is, you got salt buildup for sure.

This one is in the ground and the other one 5GL but 20 feet away and fedd same Neuts. The Mango in the Buckit has brown spots on leafs but not as bad health wise as the other one.

It's probably a deficiency in P. The growund leaches P away from the rootzone a lot faster than any of the other nutes. That's the reason most flower ferts are high in P, even though they say it's formulated for Hydroponics, in reality the values are derived from outdoor agriculture practices.