Yeah, it was the sun. Indoor flouro lighting for such small plants. Water the soil all the way through when you water, then let it dry some before you do it again. Only use that triple 8 fert if it has bacteria and fungi in it. It won't work too well without those living organisms present in typical potting soil. You might be better off to get a chemical kind of fert, a liquid, soil in garden or hardware stores (or whatever you call them in your country).