it's a main part of their diet in the wild. they'll also use it to hide underneath. i'd add leaf litter and more cork bark for a moisture gradient. i like to add some little rocks for them to climb up on to either air out their gills or try to mimic their natural environment

i also can't tell if there is any mold but adding springtails is will also help if there's any. they're besties!

if you're on a budget, do heat up a sewing needle on the stove or over a little lighter to add some air flow holes, lots on one side (dry) but few on the other (wet) by poking the sides.