The browning of the leaf margins are symptomatic of environmental stresses; these stresses can include the amount of light exposure, nutrient levels, water, temperature, or air circulation. It's certainly worth it to go over the checklist, and assuming you have optimal, or even just suitable grow conditions, it may just need to be up potted, the roots may be too bound. You could take it out of the pot, if there's an excessive amount of circling, healthy roots then you can safely assume it's too root bound. You can simply pull some of the roots apart, snip some of them (to encourage outward growth), and put it in a bigger pot with fresh potting soil. A container size to support a mature fruit bearing tree, I read from many retailers, 18-24 inches wide and deep, with a 30 gallon container being ideal. You may want to inquire with the nursery from which you bought it their recommendations for container sizes intended for longevity. 

Best of luck.