Hi, I'm a little more than 3 weeks into my first grow and around 3 of my plants are experiencing a leave problem. The very tips of certain leaves are starting to turn brown. I checked the grow faq and one of the things that it said may be wrong is too much heat. I don't think it's that though because its the bottom set of leaves on most of them. Another problem may be a nutrient deficiency which definitely might be right because I have yet to give my plants any nutrients, just water. If it is a nutrient def., are there any decent nutes at Walmart that I can easily buy? Thanks!