Answer: Congratulations on keeping your tree as long as you have! It is difficult to keep these trees healthy in the long term as container plants. So the lighting must be fine -- generally speaking, "if it ain't broke, don't fix it". In the ground these plants can handle full sun all day -- but full sun also can mean less than that, such as six hours of morning sun. In a container, they seem to do fine with even a little less than that, partly because it helps prevent the soil from overheating in summer and helps maintain a more even soil temperature in the winter.
Overwatering can cause browning, but usually this would occur at the base and work its way up. If your self watering pot is keeping the soil slightly moist but not sopping wet, then it is probably okay to keep it. Repotting would be a stress so I would avoid that if you can.
The drying out on one side only is possibly related to a mite infestation -- it is a classic symptom. I would suggest you consult with your county extension to try to get a definite diagnosis on that. If the damage is extensive it may be too late, so do not wait.
Since it is in a container you do not want to fertilize much if at all; fertilizing would make it grow faster and that is not what you want. A spring application of an all purpose slow release granular at a very low rate should be sufficient along with possibly a top dressing or two of good quality compost. If your potting mix contains a fertilizer then you would not need to fertilize the year you repot. The spikes may or may not dissolve correctly and would not cover all of the root area, so their absorption can be spotty.
I hope this helps!
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