Hey! I'm building a vivarium for green and gold bell frogs and I'm planning how to provide water to them. They're a reasonably water-loving/strong swimming species as far as tree frogs go. I would like a somewhat natural looking option if possible, and I have access to a kiln for firing. Is there any reason not to use fired clay in a vivarium? (either plain unglazed or with a clear glaze.) It would be ideal as far as shaping and utility goes - the plan would be either to make a 'bowl' to place in the substrate or to make a sort of bank shape and attach it to the tank walls with silicone (with the water area planted with emergent plants and containing sitting locations and such.)

Bonus question, substrate related: am I safe to use ABG mix with these guys? They eat by lunging but are reasonably delicate about it (I've also seen them scoop things like leaves out of their mouths if accidentally ingested.) The only feeder insect allowed to roam free in the tank is large blowflies, which generally stay off the ground, but I would assume it only takes one incident for them to become impacted. Would layering the substrate so that there are a few cm without charcoal/bark/hazardous chunks like that work? Their current substrate is packed fine claysoil with a drainage layer beneath, covered by oak leaves (I know it's not ideal but it was a short term solution that worked well. The frogs were acquired as tadpoles at extremely short notice to save them from death.)