The ph level of the water, if the PH in the water ur feeding ur plants is too high or too low, it will what we call "LOCK" out nutes making it so your plant cant uptake those nutes, which inturn will start defenecies.. n other problems . So first step to fixing any problem is to make sure the PH level of ur water for ur plants is perfect. Hydro and Soil PH levels are different requirements. For soil which it is I think ur growing in. A good level is 6.5 I like to make mine 6.6 . For hydro i think its 5.5 ?
But anything lower then 6 for soil wont do. Anything higher then 7 IS a NO NO . You can check the ph of ur water wit a tester, n fix it accordingly