When people mention not to put a UTH on the bottom it isn't just because of burning the frog. Its more that this a burrowing frog and he does this to cool off and get out of the light and heat of the sun. So if he feels warm and tries to burrow to cool off he will not be able to because the substrate is warm to, it throws them off from being able to regulate there body temperature. Think of when your outside and dig a hole the farther down you go the colder the soil or dirt becomes. Can you take a picture of the side that's clear? And is that side swollen? When you bought your frog what kind of bedding was he on there? Im wondering if he is impacted and that's what the black thing is inside and its damaged or tore something internally and he has an infection. I don't think the crickets are the problem, I think he severely impacted or he is sick with something. Did you try a honey bath yet to see if he would poo?