Help diagnosing and solving this issue

Here's the breakdown....

276w cfls mixed 2:1 2700k:6500k
Foxfarm HappyFrog Soil
Day 15 of flower
Botanicare ProBloom 30ml/gal every 3rd watering
Botanicare Cal Mag 10ml/gal as needed
Botanicare Liquid Karma 15ml/gal every 5th watering
Reverse Osmosis water
Feeding is PH'd to 6.5

I noticed the leaves starting to yellow, only at the bottom of the plant where the light penetration is weak. I also noticed that there were black spots all over the yellowing leaves and I'm also finding the spots on green leaves too. Help is needed and greatly appreciated. Thanks in advance!!

man they look so frikn nice, -the new damage to leaves that is.. im not sure what the problem is but i sure hope you get the help you need...
sounds like you are feeding and flushing properly

i would say n deficiency but its too early for it to be part of flowering here this might poin you in the right direction http://www.weedfarmer.com/cannabis/plant_abuse_guide.php

Maybe a Potassium deficiency?

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You can also check this out that shows more symptoms:

Nute Deficiency/Burn Symptoms and Treatments

could be potassium def...really though it might sound dumb to you but some MG all purposeplant food might help..that shit can be like plant medicine. it has a little bit of just about everything in it that the plant could be lacking. youd just mix like 1/4 tsp to a gallon and water it with some of it.if it doesnt fix it your pretty much in the same spot. after all your plant wont know its getting MG it just takes in whats in it. you might want to clip those leaves too.

Canabian420 said:

could be potassium def...really though it might sound dumb to you but some MG all purposeplant food might help..that shit can be like plant medicine. it has a little bit of just about everything in it that the plant could be lacking. youd just mix like 1/4 tsp to a gallon and water it with some of it.if it doesnt fix it your pretty much in the same spot. after all your plant wont know its getting MG it just takes in whats in it. you might want to clip those leaves too.

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i dont care what people say mg works i use the liquid form

could this all be caused by just lack of light to the leaves? my canopy is pretty damn thick....