It looks like you had a water issue. Never use a pot without weep holes in it. Citrus needs a good drink until it runs from the weep holes. I would think that an inside container with that small of a tree would not need water for at least 8 to ten days. I like to let the top several inches dry out before I water. Root damage will occur when roots sit in water. I recommed the 5,1,1 mix for soil in indoor pots. At least a good citrus cactus mix. It is fast draining an remains so that roots can get what they need. As far as fertilize I use osmocote plus. Has most of what citrus needs. You may need a little chelated iron....the tree will tell you if it needs it. Your present tree may be ok since you repotted and added fertilize in a pot with weep holes and it may no since we dont know if there was root damage. The program now is to keep it watered, fertilized and in the right environment. Dont expect recovery in a week....it took a while to decline and it will take time to recover. If it goes to that big garden in the sky....start over with a good grafted tree, right pot, right water, right fertilize and the right soil mixture. You should have a healty tree, blooms in short order and fruit shortly. Good luck and welcom to the forum.