Leaves Bright Yellow, then Brown and die

Indoor grow in soiless metro-mix with coir coco. I added dolomitic lime to mix during transplant to balance ph. Had/have fungus gnats and thrips. Thrips seem to be gone and gnats are on their way out after several rounds of Azatrol. Problem now is that lower leaves are yellowing, then die completely turning brown and shriveled (see photos below). Plants are in 4th week of flower and seem to be stunted. I started thinking that they may have nute-lock so I tested ph of my water which is 7.0 and then flushed out one plant and tested the water after it went through the soil and it came out as 8.4.

Could the soiless mix by too alkaline causing the flush to be alkaline? Or could the fungus gnats be eating my roots and causing this? I also thought that this could be a deficiency of N or Mg. Any thoughts or past experiences on this would be greatly appreciated.

ive got some gnats, but not a lot of what you're seeing except a VERY few amount of lower, very lower leaves doing that (my girls are doing OK otherwise).

what is the nute mix you are using. they shouldnt be growing that much more in height, you mean, stunted in bud growth?

that's the progression you see in leaves in your pics? Left 2 right?

with that coco, was it stuff that was buffered? was it the bricky kind or fine?

also - check this page out, if you havent already:

http://www.icmag.com/ic/showthread.php?t=11688

Botanicare bloom with maxicrop, silica blast, karma, super thrive. Yes, stunted bud growth.

Yes, left to right is progression.

Soiless mix is Sun Gro Metro Mix 702 with Coir:Formulated with bark, Coir, vermiculite and coarse perlite, starter nutrient charge (with Gypsum) and slow release nitrogen, dolomitic limestone and our long-lasting wetting agent.

anyone else ever experienced this or can give advice? greatly appreciated!

Just the opposite. Mine is working from top down on a JCII, started at 5-6 weeks. Now at 8wks All my fan leaves on my top buds are gone and the bud looks ready to chop but all the trichs are still clear. ???

anyone else with advice on this?

You should have posted in the Problems forum....

i'd say if its from top down you should check magnesium def or potassium def