i wouldn't suggest immediately going to epsom salts for mg deficiency (not that it doesn't help, skunk and quickee are totally correct). a lot of times nute lockout can mimic a mg deficiency. are you using correct ph water? are you growing in soil or hydro? if soil, you should check your run off ph first before you start putting epsom salts in. i always say try other ways around a problem before just adding more nutes because if you get an mg imbalance by using epsom salts it can lockout other essential nutrients. hope that helps...