hi.......qestion I have is.........
1. Did you use new soil, or did you use this soil for more than one grow?
2. Did yo measure the ph of tap water and are you giving nutrient solution?
3. How big is your light intensity??
In any way, you should be able to measure ph..........which should be arround 6.5 growing in soil. My guess is, the soil is not new and you dont control tap water ph, which mot likeley will be too high