I think one has to Die ??? :(

This looks like a middle stage Calcium Deficiency. Up your rate of CalMag. A foiler spay for immediate absorption is the best solution to a middle to late stage Calcium Deficiency. Your local grow shop should have a good foiler spray or Amazon has a wide selection. I’ve used Calcium Chloride and mixed it into a spray bottle and wet the leafs daily for 4 days and it had immediate results. I hope this helps.

Dam my bro your PH is too high. 5.8-6.2 Also. What is your RH and canopy temp?

Severe calcium deficiency. It is not the end of the World! Remember too.......what is showing in the leaves now, is a direct reflection of what was occurring in the root zone 2-3 weeks ago. No need to kill it at all, it is not contagious. Up your cal/mag dosage, it is very hard to overdose with cal/mag, so be quite generous. Damaged parts will not recover and things may get worse for a few days, before settling down and then hopefully stabilizing and not get any worse, but it may take a week or two for this to occur. This plant also looks quite hungry for potassium too.

You don't need to kill it, its not contagious. its a issues with the feed. you need to find out your EC and PH and go from there.

What is your run off ph and ec, tds, or ppm? Are you getting 20 percent run off each feed? If not it may have a salt build up.