Materials to put in tank

So, I've been planning to get my own axolotl for a while now, and have done a large amount of research. There's a great breeder in my area, I have a spotless 10 gallon ready, and I will probably upgrade to a 20 or so when I get my hands on it. I'm going to buy a Topfin internal filter, ad a fine sand substrate.

I really want to have a garden aesthetic in it, and so I found a terracotta pot around the house that had previously been holding pencils, and that is now soaking. Some bubbles floated up for a few minutes- I believe that's because it is a porous pot, but am I wrong?

The other problem is that I've found some bricks, which have been in thirds for a very long time, so they're no longer sharp. The bricks are about a hundred or so years old, taken from the Ohio river. I only selected two, which are soaking. When I put those in a bucket, there were a lot more bubbles, and one of them even fizzed out bubbles when I took it out of the water, although only for a moment.

I'm very skeptical about the bricks, but pretty confident with the terracotta pot. What should I do/use? Any good and safe alternates?

It just sounds like air coming out to me. I have used old bricks from the Hudson river, myself. And terra cotta. Both are porous.

Alright! Thank you.

I have yet to check on the bricks, but the terracotta pot, which has been soaking, had turned the water a brownish-orange. I'm pretty relieved that I soaked it. I'm going to switch out the bucket's water, soak it some more, and hopefully be done. Is that all safe?