Sour Kush slow grow..

Whats good. I have noticed that my sour kush is growing very slow compared to my other plants.. I also noticed that the main stem has some white stuff on it. I am not sure if it is fungus, mildew or anything in that category. I am also noticed that some of the tips on the leaves are yellow/orange. I bought it as a clone at one of the local dispensaries, healthy. I am feeding her on the foxfarm nutrient schedule. Does anyone know what that white stuff is? Could it be why that plant is not really responding? Any information will be gladly accepted. Thanks.

maybe ur soil level is just falling like normal.. ive noticed some of my clones get the white bubbles on the lower stem its just a little air getting in.. not sure if thats what it is because i cant see the picture too well. the other shit is nut burn cut back on the feeding schedule. im feeding at 1/4 and i still burnt em a little bit