Stonerdanswered grow question 4 years ago The problem might be the low temperatures in your grow space! 21 degrees Celsius is quite low for a seedling, they usually need 25-28 degrees with some varieties even 22-26.
You should always aim for a higher temperature during that early stage. About 23-24 degrees would help your seedling grow better.
Also try giving her about 1 liter of water with 1/5 of the recommended fertilizer dosage.
Hope this helps! Good luck and happy growing :)