looking good man. im subbed up.
if when you put the metal in the soil you broke some roots off it may have stunted them for a day or 2 while they regrow them roots but it shouldnt have been anything major.
have you got your DIY CO2 hoocked up? i recomend it. its not the most eficient way but it helps and its noticable help.
aas far as the growth on that plant, possible genetic issue is what i would chalk it up to.
time to transplant maybe? this can cause growth to slow down as the root system reaches its max accupancy in the container, a plant wont grow bigger than its root system can brovide for it. i had a issue on my first grow, 4 weeks in they just stopped growing, transplanted from 1 gal containers to 5 gal buckets and a week later i was noticing 1-3 inches of growth a day!!, if you can remove the root bal and all the soil stays formed to the shape of the container due to the roots holding it together its time for bigger containers....
this is what mine looked like last night...way overdue, i would proba have about 4 inches more of growth had i dont the transplant a week ago
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