ok, it sounds like nutrients, added to much nutrients. Make sure you are using the instructions and dont give more than what it says, actually give them ab out half of what the direction say. To fix this, you need to flush em out, not sure how many plants there are brown spots on , but flush the ones that have them. Use ONLY PH'ed water, NO NUTES. Flush with 3 times the amount of your pot size. For instance, if you have a 2 gallon pot, flush with 6 gallons of PH'ed water. Tha plants WILL come back tomorrow if not today. Also, the brown spots will always stay there now, so that wont go away, but if will clean out the soil...... let me know if this helps....