leaves have yellowed or burnt heads

Yellow tips on sprouts is usually due to more nutrients in the soil then the plan can handle. Too much light can also cause fading and yellowing of new growth. First thing first, check and make sure ph is where it should be. Second, at this stage of growth a 1000 watt light should be about 22 inches away, maybe more depending on power settings. Lastly, make sure you are not overfeeding, and make sure to give plain ph'd water after every 1 or 2 feedings, with runoff everytime. Happy growing.