im no pro but maybe consider foliar feeding epsom. are you sure its mag def and not something else like ph being off. if you have multiply plants going you may consider dropping your ph down to high 5's and just watering one plant. then see how it responds. man, ive learned that its hard to get definitive answers on here and its best just to experiment with different things. another option would be to buy some calmag plus and feed your plants that. make sure your lights arent too close.