leaves purpling and exhibiting chlorosis

Hi all,

My current grow is 5 weeks into flowering and one of the plants in particular is exhibiting leaves that are turning dark purple near the veins, and then eventually yellowing/drying out starting from the outside in. This is affecting the plant from the top down -- only the first few nodes are presently affected, but it keeps relentlessly affecting the next-lowest set of leaves.

I would normally just assume nute burn, flush and be done with it, but I have been feeding all of my other girls the same, using the same soil, etc., and it is only this one plant. This lady is by far the biggest and has the most budding sites of any of my plants, which made me think that perhaps it could be a deficiency instead of a burn ... ? Also, I have dealt with nute burn / lockout before, and it seems like this is a different color pattern. About two weeks after the first signs of darkening, the leaves start to get crispy and yellow, but none has actually "died" yet.

The pH is about 6.1 for all plants, which is lower than ideal, but not catastrophically low, right?

It could be the buds sucking all the plants nutrition from the leaves. as long as buds are ok then it should be alrite

they look really hot. what are the temps

They do look rather crispy, no? However, it is a CFL grow (460 watts total) with plenty of ventilation, so the temperature never gets above 75. I decided to flush this plant and add a little bit of wood ash from my fireplace to up the pH a little bit -- I figured it couldn't hurt, though I don't know if it will help either.

These plants are all from bagseed, and I'm pretty sure this one has different genetics than the rest. Instead of concentrating most of the growth on the tops, it has sprouted literally hundreds of tiny, slowly-maturing bud sites. For a long time I thought it was stunted, because the buds are so much less mature than the others, but it just seems to be going very slowly. It could be that it is using up all the energy for the buds, but I would guess it has at least another 4 weeks before harvest. That's a little bit early for the leaves to wither up, isn't it?

Maybe I should just stop freaking out, eh? Thing is, it seems to be happening pretty fast. A few days ago it was noticeable but not worrying. Today the plant definitely looks sick to me.

Could it just be phosphorus def from all the buds? I have never seen a pic that looked like this in an MJ grow guide, but doing a google search for "phosphorus deficiency" turns up pictures of tomato leaves that kind of look like this.

Example:
http://greenartz.com/wp-content/uploads/2008/05/tomato.jpg