are you sure the flushing didnt turn your plant yellow? you should still have nitrogen but in small amounts when flowering. if your ventilation is good you can keep the 400 closer. mine is at 6-7 inches and i watch for growth and raise it as needed. good ventilation is key here. ok, read the mediocre part again. you should still be able to keep it 9-12" at least, unless you moved it from cfls then take some time to get it used to the brighter lights.