Athosanswered grow question 6 years ago You are giving us absolutely no information to help us diagnose your issue, not even pictures under white light. It could be anything wrong pH, over watering, nutrient deficiencies, low temperature, lights too close.
That been said, the most likely cause, since it began after the switch is lack of grow nutes.
You see, after switching to flower, the plant has a growth spurt that needs massive nitrogen and potassium.