use mylar instead of foil, foil creates hot spots and can burn your plants (though I don't think you have to worry too much about that with those lights). Get those lights closer to your plants, lights that size can just about touch your plants without problems. Why do you have a heater in that box is it really that cold, the small amount of heat coming from the lights in that size box should keep the area warm enough unless you are in a very cold room. Do you have any lights above the plant, it looks like you are using some sort of red tinted light? As for the nitrogen deficiency get a good nute for feeding, its that simple, you can also get cheap ph and npk testers at most stores so you can really find out what you are lacking or may be overfeeding.
