Calcium and Nitrogen deficiency?

The yelllow leaf tips indicate nitrogen toxicity, not deficiency. Other than that you have a cal/mag deficieency, with possibly a need for extra potassium too. One cola can not be more deficient than the rest of the plant, all nutrition is used equally throughout the entire plant. Being a lower branch, these show the deiciencies first, that is why it is slightly paler than the higher up branches, as the plant takes from the older leaves to give to the newer leaves, but it is potassium she needs, not nitrogen. Adding a P/K booster along with some more cal/mag should solve your problems.