Mmmmm i'm going to go for high amounts of nitrogen the pot your useing looks to me to be about a 1 or 2 gal pot's so if u have be over fert these lil ladies its super hard on the root system's witch can be seen on the sucker leaves and yellowing new growth but i would not be to quick to rule out high heat also like others have sayed....give them a good flush is something i would do and re do your feeding solution something more watered down