Yellowing & browning with brittle leaves

Hey everyone.

Im around week 8ish into flower and have been seeing this yellowing/browning with the leaves turning brittle over the past week or two.

Just did a res change with last batch of nutes before flush. Im thinking calmag? New res has extra calmag just in case i was correct on that guess.

Roots are healthy, temps stable high 60s low 70s 40-60% humidity depending on day

Calcium deficiency at the least.

i have similar unresolved issue... what about black spots and taco leaves?

Here