what're u growing in? coco? coco locks out calcium i think and its reccomended to use 3-5ml per gallon every watering or so
but if its only those few bottom leaves and they aren't getting a lot of light, it may be because it needs light.
also id check into possibly leeching your soil and then stepping back onto the nutrients, maybe it needs the salts cleansed off the roots and its locking something out