Over water?

You keep saying your watering them every day, I cant believe a plant that small is drinking that much and looks like overwatering to me. Why would the size of the pot matter? You want the roots to have to reach for the water not always be wet. If a large pot has a dinky plant in it the bottom may be wet all the time by watering everyday, I had a few start off very small compared to the rest and transplanted them to get them into different medium and was suprised to find the roots were reaching the bottom of what I thought was a large pot compared to seedling size. IF you have holes in the bottom of the pot and its draining fast make sure you feel it dry on the bottom not just the top of soil. Sometimes I think we try to much instead of just leaving the babies alone. Anyway good luck on the grow

I would say it is the light source, your lamp is good for vegging but can be too hash on the little seedlings, try use 3 cfl bulb about 3 inches from it. You should not need to nut them at this stage.