looks to me it seems to be an overwatering issue. make sure drainage in bottom of pot is working properly and just cut down on watering for a bit to see if it clears up.
plants that size in pots that big shouldnt even need to be watered but every 7-10 days in my experience. use the weight of the container as a guide to when they need water. if the container is light when you pick it up then its time for some water, if its heavy and you can feel some dead weight (water weight) then it can go longer.
when water leaves the soil it provides O2 to the root system, if you constantly are watering then your depriving the roots of O2.