Im not sure about the soil you are using. I seem to have read a few people in this thread have/are currently using it. From what i gathered from the thread is that the soil is kinda pre-charged with the needed nutrients to complete a cycle, with little to no additives correct? Im not sure if you have a PPM or PH meter. I remember people saying " When in doubt, flush it out" Not sure if thats the case with the soil you are using. It looks like its only near the top also correct? Could be burn from the LED if its taller than the rest of the plants. Maybe try to grab a gallon or 2 of spring water from the store. It has some of the micro nutes in it that are stripped when distilling. Usually it is pretty close to PH neutral as the distilled. Good luck! Keep us informed.