hhhmmm, your problem could be one of many my friend, however i do not think its nute burn, organic nutes are much more forgiving than chemicals, you have to really lay it on to burn em, whats your ppm? what is the temps and humidity in the room? possibly some heat stress, high humidity stress, did you check your roots for damping off? although i do not know your condition, i would recomend silica blast to anyone doing such a confined grow, as yours, silica helps strengthen your plants cells making them much more thick and robust, it also cushions the effects of harsh enviroments such as high temps and high humidity, it also helps the plants fight off wilting, hope that helps and good luck