The most common problem is over watering.
The second most common problem is under watering.
I think you MAY have a couple of things going on here:
1) Over fertilizing - nute lock. Solution; flush with clear water two days then do a half dose of fertilizer for a week.
2) Over watering. Solution; always (as in always) let the soil (medium) dry out before watering. These girls like to be moist - but if you keep them WET all the time = problems. I water and feed mine every three days, but it depends on the type of medium you have, and the size and type of your pots. Your results may vary - learn YOUR girls. They are all different - each is an individual with different appetites and needs.
3) Micro deficiencies. Solution; CalMag half of recommended dosage every two weeks. (Real easy to overdue CalMag, be careful)
DO NOT do all three of these at the same time. If you have been keeping the soil wet, then do #2 and start #3 next week.
If you have been letting them dry out once in a while, then do #1, and a week later do #3.