the tips of the bigger, upper leaves are discolouring and curling. i'm not fertilizing, but i'm using fortified self feeding miricleGro soil. what's up?
What kind of lighting are you using? Sounds like the source of heat could be too close, that or a watering problem. How often do you water? Could also be the miracle grow stuff...miracle grow soil/ferts tend to have a high-in-salt content, which can damage your plants.
I too have been told to stay away from Miracle Gro potting soil for this reason. I used it once and got a couple of nice plants. The problem was that the top cola started to go moldy overnight. This only happened when I used the Miracle Gro. Next time use an indoor potting mix and always replace it after each crop.