I used to fed them 1 time with nutrients and next without, and its true I started to watering only with nutrients, but I also brought her close to the light so thats why I'm confused, so for now just water till this yellow tips go away?
if it were the light, you would also see curling of the leaves as they slowly burn up.
chances are you have just over fed them at some point.
i would just wat n see how she go's
the yellow tips wont go away, there there for good, you just dont want to see the yellow spread to the rest of the leaves or you may find you have to feed it as it wll be a nutrient deficancy