New pet death head cockroach problems!?

Hi i got 3 new death head cockroaches 2 months ago and i have never owned them before and i think there alright but im not sure and i want to be sure if im looking after them alright


I got a large exo terra tank as the tank


I filled it with exo terra plantation soil about 3 inches deep


I added a harpheaven plastic tree hiding stup as a hiding spot


i add a soaked cottan wall ball in a rock dish for water (i dont actually leave any water i just wet the cotton all ball and place in dish i hope this is okay)


i feed them on fruits and veg like carrots, bannana, apple, tomato and lettuce (cockroaches personal fav)


i provided them with a rainforest heat mat although the tempreture is not a 25 to 30.c its at 20.c i hope this is okay (is there any way to make it a little hotter


Another thing im kinda scared about is the cockroaches have dry soil on there backs is this healthy and is there a way to take it off also the cockroaches i have only ever seen eat a few time so i get a lot of wasted sol



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