I believe it's the nutrients making the leave tips a little bit yellow and I will be keeping a very close eye on this, she has just started flowering and I have just introduced my (biobizz bloom) flowering nutrient during watering at 1/4 strenght.... humidty is normally kept between 35 - 40% at all times which is decent enough ,,grow box temps vary from 75-80 degrees and ventillation is managed by a nice 9inch fan blowing cool air around grow area.. thanks for the advice anywayby the way, what is the humidity level in your grow space? keeping it enclosed with a little container filled with cold water should help bring the humidity back up if you are on a tight budget.and make sure you have good airflow in there as well...