Switch to de-chlorinated tap water. Im betting you are overwatering them, 5 gallons of medium is a LOT for a plant that small. This is causing root issues which is causing nutrient issues. If i had a plant that size, it would be in a 1 gallon pot and i would be thinking about transplanting it into a bigger pot in a few days-a week depending how much i trained it. How much and how often are you watering?