Do you have proper drainage in that tub? Looks over watered. Let her dry out between waterings. That will get more O2 to your roots. What ph are you watering?
Yup. I'd have to agree with warble, looks over-watered. What brand of soil/soiless are you using? If it retains too much moisture for too long it will cause the same thing. I like my soiless to dry within a couple, maybe a few, days.