I'm not a hydro guy, but I did notice a couple of things...

High output fluorescents aren't effective beyond a few inches. So if the Mylar is obstructing airflow, I'd ditch it. (the light has to travel to the mylar, then bounce back to the plant) Flat white paint is the cheapest alternative over the long haul.

From what I understand, it looks like your ph is a tad high for hydro.

Using fluorescents, the lower regions of the plant don't recieve enough light for vigorous growth, and will look like that till you get more lumens on 'em.

Do you have a ppm meter to check reservoir?