Harlequin has been unavailable from the breeder for at least 12 months, elev8 seeds are a scam , they also claim to have Gorilla Glue4
seeds.
https://www.rollitup.org/t/gorilla-glue-seeds.878049/
What is that rubbish they are trying to grow out of? Never use poor quality soil when growing cannabis.
The medium is the cause of your issues. Try this next time you can get it from the hydro shop, very simple and great results.
Its early in the season so it could get massive 2lb + , you may have to re pot at some stage which could be difficult.
Someone could just wheel it away one night, i would have chain on the cart.
You say another 8 have done this then just died?
You need to change strains
dont use that one again , be careful when you re pot and when you water make sure you drench the medium with runoff.
You can write this one off, looks weird.
These plants are very sick because of major N def, 100ppm is not working not even close.
You need need to jack up the nutes x5 and hope and pray the sick little fuckers can recover.
The soil is no good for seedlings or anything else, it looks crappy. Dont re pot yet it will make things worse just feed them some veg hydro nutes at 1/2 strength for 2 weeks then full str.