I have few carrot plants. Two weeks ago I added much needed fertilizer, mostly they are doing good. I pulled out 5 recently, 2 were very pale, 1 was tinny and two were medium-sized and very tasty. Now there is this yellowishness on the leaves. I added Cow Manure, Calcium in the soil and calcium to the leaves, Sea Weed to the soil and to the leaves and some Epsom Salt a week after fertilizers. The plant gets good sun all day long, I sometimes add a shade cloth during from 12:00pm-3:00pm.