When I was growing my meyer lemon in ohio I had it under full spectrum flourescent lights. Either just a regular light bulb used for lighting but full spectrum. It should look bright white to your eyes rather than the orange glowy ones which or not good. Or sometimes I used a sun-glo reptile bulb which was also full spectrum bright white but also had some UV in it and slightly different spectrum than the other full spectrum so just gave it more variety.
I watered it with tap water and everything. It was healthier and bloomed more when outside, but meyer blooms year round and I got blooms in winter and the tree was overall healthy. Like I said not quite as happy indoors but I tried to keep it near and window and I had the flourscent on for like 12-14 hours. Seemed to do fine.
You could have salts/minerals building up from tap water. You could do a flush by buying a couple gallons of distilled water, take it in a sink or outside, let the water run out of the bottom of the pot- taking the salts with it. Citrus should be tolerant of soil thats a bit alkaline or bit acidic. It's not that picky about acidity. But tap water if its flowing in, but not flowing out, over time whatever minerals or salts are in it might build up in the soil and need flushed. Or it may be the LEDs. I have to agree with W. I used fluorescent lights and they did fine.
The only thing with a flourescent bulb is it is so weak you need it pretty close to the plant if possible or try to use reflective surfaces to reflect more of the light on the plant or use multiple bulbs. It was getting a more diffuse type of light in the winter on mine, but seemed to do alright. I put it outside as soon as temperatures were warm enough. It was inside as little as possible, but that still was like four or five months out of the year in ohio and I was getting lemons on it. If I kept it indoors year round under those conditions it probably wouldn't have done too well though.