Have you foliar fed them or spayed any water or mister on them ? I got a buddy that just foliar fed some and he thought everyday was okay but after 3or4 days the started to look like that and then got worse.

If not I would just give them all R/O water and no calmag either untill you see a difference.

Oh are they too wet ? My bro has been fighting root rot and that is the look on the leaves before they start turning yellow. You may want to dry them out.