Building a soaking pool

[Xubby]

I made a half a gallon "pool" out of a tuperware style container (supposedly BPA free, if that matters) which has polystyrene cut into various shapes and is held together by black silicon. There is also a layer of silicon on top with some cocofiber stuck into it, though a lot of the fiber has fallen off. It's my understanding that all of these are safe.

I've made a couple of these, but the oldest one is in a tank with a large woodhouse toad, and has recently began to have a slight oiliness on the water surface. I can't tell if that's related to the toad, the cocofiber decaying, or something else I should be a lot more worried about. It's not iridescent, like normal oil can be, and I'm not sure what I'm looking at. I change the water pretty often, but it will usually reappear if I let the water go unchanged for two or three days. There's a lot of springtails around there. Any idea what this might be?

Either way, I'd like to build something a little more permenant than that, but still have it be nested in another container. This would let me take the whole pool out without worrying about having the soil around the sides collapse back in. Does anyone have any suggestions for improving the materials? Concrete or grout sounds nice, but I'm worried about how harsh it might be on a toad or salamander belly. The plastic frame invariably flexes under the weight of the water, allowing water to sit under the foam. While making a couple of holes to ensure it drains properly is working fine, I'd like to not have to worry about that. All and all, I just feel like there's a lot of room for improvement.

The sizes of the pools would vary from about 16" x 9" to maybe 7" x 10", with the deepest being up to three or four inches deep at the deepest spot.

[DigitalPunk]

Here is a youtube video of a guy who makes great custom ponds and waterfalls for reptiles and Amphibians. He has several style on his channel

https://www.youtube.com/watch?v=Rgh9jXme6OE