Maybe it’s a light, but I’m not seeing any brown spots which a bad calcium deficiency would show.

It more looks like you have fed it to much p/k & not enough n.

Don’t switch to bloom ferts till your two weeks into flowering feed it veg ferts for the first two weeks

You need them to have enough n to make it through the stretch period

If the ones yellowing you think has a cali deficiency it may be that plant doesn’t eat as much as the others & you locked the n out with to much p/k

How close is the light