A lack of nitrogen would fade the lower leaves yellow to send nitrogen up to new growth. The nitrogen cycle involves the creation of amino acids and is very mobile within the plant. There is no such thing as a cal-mag deficiency. Calcium and magnesium are two different elements that show completely different symptoms when lacking. Calcium becomes part of a cell wall and is not mobile like nitrogen or magnesium. A lack of calcium will cause physical damage that creates little brown spots on old and new growth, all over the plant. The damage is permanent. Magnesium is needed to form chlorophyll and is mobile within the plant. A lack of magnesium causes interveinal chlorosis (yellow tiger striping between leaf veins) that is not permanent damage that can be fixed. Similar to potassium, but potassium just fades the leaf blade edge keeping the center of the leaf green like your plant. Nitrogen and potassium are the two most abundant elements needed by the plant throughout it’s life. Any root stress or damage will cause either element to show a deficiency first. Potassium has a wide pH range so if your pH was out of range, other elements would also be locked out. Under and over-watering are common issues that prevent enough potassium uptake.