get a pic up i had the same problem...sounds over watered but maybe lack of nutrients..soil or hydro? how big is ur pot or hydro tank? if its a 3 gallon pot what i use water it every 4days or so with 3quarts a lil over half a gallon
if it's not yellow, it's most likely from over-watering, although it may be from under-watering but it's more uncommon. how often do you water your plants and what kind of medium are you growing in? the more details the better.