Please help with valida placement. It is one of my favorites but just cant get it to take off. The stem is a light brown and tips show light blue. Its currently in the middle of the tank with 2x250w 14k MH and 1x 400w 20k mh not running at the same time but with a half hour overlap. Growth has been slow to none. Tank is 660mm (25inches) deep. Lights run for 5 hours and 20k for 1 hour.