Growth halt

First and foremost, don't overwater them... wait until they are light as air and then give them a drink of water. Even though they are very young, you might want to start them on a bit of grow nutes - say 1/4 strength to start out. Don't worry about the cotyledon going completely yellow - that's natural and they'll fall off eventually anyway... but you're going to need some NPK in there to help her grow and turn green... And oh btw... get them OUT of the clear plastic pots... Cannabis roots need complete darkness (so the "clear" doesn't work) and they need oxygen at their roots (so plastic doesn't work, either)... you're opening yourself up to some root rot with the plastic and poor growth with the amount of light getting to the roots... go with fabric pots... black fabric pots! Cheap and resuseable (if you thoroughly clean them after using). Good luck!

Mono potassium is for flower mate, there could be milion of mistakes you making .... Find a book and read it, then do something.