Plant just stopped growing

Hi All,

Im new on these forums, used to post on rolitup but cant seem to access the site any longer, wasn't a regular contributor by any means and generally read both forums.

I've been growing for personal use for about 4 years off and on, I would same i'm pretty clued up on the subject and have had some great and successful grows in the past, certainly not a beginner.

Currently I have 3 plants growing indoors under a 400w HPS with fans and all the bells and whistles. Strains are Norther Lights, Bubble bomb and Amnesia. all auto flowering and under 12/12 light schedule (yes not the most efficient but i prefer it)

The problem is with my Amnesia plant, she has literally not grown at all during the past 8/9 days, not an inch. the last watering I did was about 2 weeks ago with a weak nutrient solution, she then quickly developed 3 sets of true leaves and then stopped. The medium is coco and perlite with about 5-7% vermiculite, the soil is still moist but not wet so I doubt its a underwater issue however the two other plants are growing in Perlite and vermiculite mix only, which is what ive always used with great success, could this be a problem with the medium I am using? otherwise the plant looks healthy and there is no physical evidence of a problem besides the slight downward pointing leaves, could this be over-watering as medium is still moist after watering 2 weeks ago.

More info:
Strain : Amnesia auto
Lights : 400w hps (12/12)
fans : induct outlet and inlet
temp ; 1-2 degrees hotter than ideal but other plants are showing no issues
PH : fine, ranges from 6.5-7 and other plants get same water
Nutrients : also fine, watered the Amnesia with a weak solution 2 weeks ago which then prompted rapid growth until 8 days ago when it stopped.

I've run into plenty problems in the past, specifically in the beginning days however I've always managed to trouble shoot and resolve the problems using the great info on forums like this but I'm seriously stumped on this problem, I think I've covered all areas at least I hope...any ideas what could be going on here, what can I try to troubleshoot ?

Below are pics, she been like this for 8/9 days, nothings changed. thanks for input

 

Well im using a standard chemical nutrient 3 part mix (micro, grow and blossom) have been using this on all my grows for past 4 years, I could take the plant out and put it under cfl's to see if its maybe the slightly high temperature but then why are the other plants thriving? maybe amnesia strain just very sensitive to temperature?

 

Seems the medium was the problem, My mistake, didn't flush or clean the coco before use, flushed her thoroughly over weekend, a lot of brown milky run off in the beginning, im guessing that's what caused the problem, hopefully she recovers somewhat now but not expecting much of a yield.