Something similar happened to me. The two chronic plants below (the two in the middle) are the same strain, GSC, also from bag seed, germinated the same day, and shared the same lights. The only difference was that the smaller one started off in a smaller planter, and didn't even begin to think about trying to catch up with the other until I transplanted it into a 5 gallon soil bucket. Oh yeah and I first let them germinate in regular old Arizona soil... Both grew fairly slowly until I got them into soil of the correct PH. The big one is now 20" and thebsmaller one is 10". Which leads me to the fact that you're using a hydro setup. Have you been balancing the PH daily? Because the roots won't pick up the nutrients unless your PH stays between 6.0 and 6.5, and that could be a reason a plant's growth might be stunted. Also, not all seeds, even sometimes seeds from the same bag, are created equal. It could just be that one was a better seed. Just trying to troubleshoot, cuz sometimes it's easy to forget the simple crucial stuff. Nice ladies you've got there, and hopefully you can figure out your stunted growth problem soon. The best of luck
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