I think it is too small of a plant for too big of a pot and too large a volume of soil that stays too wet too long.
I would transplant these little guys into 4" pots with sterilized potting soil. Where have they been growing? What type of light are these guys getting?
Stop watering so much for sure.
They need fertilizer, a balanced fertilizer such as Osmocote 14-14-14 extended release and use HALF of what the directions say.
Have these plants been moved out of doors in the sun from the indoors?
I would get 4" diameter clay pots, sterilized potting soil with no fertilizer, no water holding gimmicks such as sponges or gels and transplant these into those smaller pots.
Look at their roots while you are able. Are they all bright white or are some transparent, brown, mushy? Keep these guys in a stable environment. Artificial lighting would be good. 300 watts or more, fan turned on 24/7. 18 hours of light then darkness. Water only when the plant and soil and pot feel obviously lighter than when watered. Don't water on a schedule. Water only when the soil is much dryer.
Small plants in a large volume of soil in a pot are not able to suck up enough water to keep that soil full of air. No rocks at the bottom of the pot, nothing but sterilized potting soil in the pot other than the plant. Leave 1" from firmed surface of soil to rim of pot.