Hmm.. the leaf tips now are covered with necrotic patches.
I'm wondering whether I should flush the 2? Pretty sure it's not MG as the yellowing/browning is moving up the leaf instead of circling the outside, though it could be nutrient burn.
Basically it's a matter of whether it's a PH lockout of N, nutrient burn, or rather whether or not to give them N on the next watering.
I think I'll be flushing them tonight and add a dash of epsom salts just in case.