weak undergrowth

First off I have been growing long enough to know I don't know everything, I tend to do a lot of research and read. So lets cut to the chase. Of my three plants this is the only one that has a very weak undergrowth, I started flower one week ago from today, I cleaned up the under canopy already, I am not a heavy -defoliator. But this one problem is bugging the hell out of me all my plants looks GREAT!! I have been using FfOf soil amended with happy frog dry ferts, Natural organics CalMag and I ph down with Big bloom and and now Tiger bloom. But I am noticing this one plant has weak as undergrowth , Is it a deficiency or is it lack of light? I used LST for the entire grow to open up the canopy. I threw away one plant because of this about a month ago, the entire canopy was beautiful, but every thing underneath was just weak looking. also a side note, the breeder says that it is not uncommon to get slightly red stems with this breed, Hurricane, mammoth, and hemlock, all have the same father L.A Confidential

Bump.

So It is one full week into flower and I did a major defoliation of my fan leaves. I am trying to get some light to my lower new growth. I know the rule is to not do any defoliation in flower..

My first thought was root bound plant but then i looked at pics and saw your pots. They seem to be a good size for that size plant. It's pretty obvious that the light isn't penetrating enough. You can tell by how droopy the lack of lower growth is. What's your lighting set up? How far away are your lights? How is the tempature? If it was my plant I would strategically take off about 25~35% of the fan leafs (I know some people don't recommend it but I have seen great results from defloration.).

I have been using T5's 12 bulbs 4' for three years now. Honestly with all the fan leaves I dont know how any light from any kind of light could have got through. temps are 75- 80 and the distance goes from 12" to about 4 " then back to 12" now that I cleaned the fan leaves up the growth is already looking good in just one day.