Hi People, i wonder if anyone can help me with my growing problem. I have 20 plants growing in the third week under 24 hrs of light.They are all in 70% organic compost and 30% pearlite,with room temp never going over 28DC.All plants are female made up of 10 Big Bud and 10 White Widow.What i need to know is what is the most common cause for the leaves turning yellow.I have no clues as to whats going on as this is my first grow. Please see the pics i have posted. Can anyone help????????