Question
Some leaves have yellow veins, balance of leaf is green.  What is causing this.  Does it need some special nutrient?

Answer
Hi Bettye, I have a feeling this citrus is getting too much water and drowning.  Foot rot possibly.  Make sure there is not mulch under your tree, good drainage, maybe a once a week watering.  You do not give a lot to go on so try typing in foot rot citrus and look at the photos and compare.  kathy