Dark leaves! :O

[Sophomoric]

Hey, i have a small problem with my plants - i've been growing for some years now and would consider myself pretty knowledgable; however this problem is proving tougher than i thought.

Conditions - my plants are currently sitting in an enviroment where the temperature doesn't exceed 24c and doesn't drop below 22c - humidity is balanced at around 60 (dips below and goes above sometimes but 60 is average)

Plants are sitting in light soil, mixed with a small amount of vermiculite to deal with the insane drainage of the soil i decided to test.

The problem:

Leaves lower down on the plants (all 20) have begun to twist (not severally) and darken (becoming "thin" to touch) once they have twisted and become dark eventually they begin to die and go crispy :s My initial diagnosis was... Phosphoruous deficiency without a doubt, boron has similar effects however plant stems and general plant health remains perfect apart from the twisted/darker leaves.

What i've done:

As soon as i noticed the issue i began a foliar feeding regime with a specific foliar feeding solutions rich in all macro and micro nutrients. New growth appears to be perfect and 100% healthy with no tip burning or curling however... i do believe the problem is still spreading up the plants: so.... HELP!

(when growing in soil i do tend to lean towards under fertilization)

[Ganja Guerrilla]

can you post pics?

[smokingaces]

sounds like the same problem im having but i use a hydro system however i too chemically feed my plants. so if its the same problem could u be over feeding them a certain nutrient?