Soil grow, so that could explain some of the slow growth.
PH has been solid at 6.8 almost the entire time.
I'm pretty sure yellowing occurs when there is a lack of light. put some other plant out of light for 2 days and you'll see it.
Nutes haven't been a problem other than a slight over that I quickly flushed, but growth was slow before this as well. I expected a 1-2 week pause after the over-fert/flush and that's exactly what happened. Plants were a very healthy 12" by that point tho still 2 mo in to grow.
Light meter test was interesting. On an arbitrary/relative meter scale between 0 and 10, here were my rough findings.
The lower wattage (14W to 42W) all put out about the same amount of light at 1" from the bulb. Between 6 and 7 on the meter. As distance increased the meter reading dropped significantly. 1' from the 42W bulb read only 3 on the meter. And 2 feet from the bulb read a big 0-Zero.
Testing the 400W HPS about 1" from the bulb the meter reads an 8. 18" from the bulb, approx where the plant tops are, the meter reads strong 6 to 7.
3 feet from the bulb reads a 5. 4 feet from the bulb reads a 4 on the meter. 10 feet from the bulb I get a strong 2.
I could do some documented tests. These numbers are mostly from memory. Observation and the meter confirms that any more than 12" away from a CFL does nothing where you still get useable light up to 3 feet from an HPS. This has probably already been established.
I personally like my HPS(top) and CFL(under/side)
Juicy 500W or so for my babies.
I'm a new grower anyway. This is my very first time and so far so good. I've made mistakes and it's possible that some of the mistakes caused a slower growth, but given the strenght, girth, internode spacing, and now the resulting mass of buds after 2.5 weeks of flower. Well, I can't complain. And CFL's sure as shit did a great job in veggin very healtyh plants when they were<12". That's for sure.
Smoke more HERB. Cure SICKNESS!
wow that was a lot of info i have a few question i have not yet in my growing experience had yellow leafs due to a lack of light not saying it cant happen i just have not ever heard of it or read it or seen it i have seen this though in nuts deficiencies also have seen very slow growth due to poor PH balance due to the fact that this is a major contributing factor in how much nuts it will absorb/eat has any one else heard of this ??
i am interested to know the result of the light meter what exactly did it tell you ???
were you growing with soil or some other method ??
the reason i bring this up is because i have found that cfl's tend to work better when the roots get a ton of air flow which is why i use an airoponics method similar to the bubble bucket the roots flip out and my stems are fat as hell which is all part of the nuts delivery system .......
i think if you are going to grow for production then
HID is the way to go but that is a different thing because you are going in to it like a business and you have the correct funding and all of the appropriate equipment IE: spare bulbs and ballast extra timers and the such but for for less then 15-20 plants in my opinion CFL is the way to go for the record there are many thing that can be done about the consumption of power when using HID when i was growing a few years ago i was in production and my target goal was to produce an OZ of product for $30.00 dollars or less...
EVERY THING I HAVE SAID HERE IS A LIE AND I HAVE A SICKNESS OF THE BRAIN THAT CAUSES EXTREME LIEING AND TERABLE SHACKING OF THE HEAD.....
Uhh if I do 1/2 that well with that much space under HPS, I'll be a happeh pothead. 
