Im watering every 3 days aprox.
HPS 250W for 4 little chics (between 40cm and 70cm) of course 12/12
Im using tap water on all plants and other chics dont have the problem.(i cant know whats the PH.....i CANT get the equipment for pH testing... :S)
Humidity is @60-70%

Its possible that the rootbound issue is happening, BUT i dont understand HOW i have a rootbound one (im SURE she is rootbound because she hasnt grown in a while and she is in a very little pot) and she doesnt have this problem.(shes flowering AMAZINGLY and looks sexy )

The one with the problem is aprox 60cm high and she lives in a 4 gallon pot, so i dont think she is rootbound yet.