This thread is couple years old so curious, have you guys had any long term success with a firebrick formicarium?
I've made a couple over the years from K-23 and most ants just simply prefer other materials. I've kept Crematogaster and Formica species in Firebrick, and both colonies did better in other formicaria. As the ants live in the nest, silica dust (which is harmful to the workers and certain stages of brood development) will accumulate, eventually leading to a sluggish colony with no brood. The low humidity of the material is also another factor contributing to low brood development.
I would also advise against soaking the brick with a live colony inside to hydrate the nest. Any water in the brick will be saturated with the aforementioned silica particles, which will harm or even kill the workers who drink the water. Because of this, I would recommend a water tower over direct hydration for FireBrick. Providing additional water sources in the outworld may allow species who don't chew the nest up to be kept long term in K-23 FireBrick.
One possible solution to the loose silica dust would be to coat the interior of the firebrick chambers with grout or something similar in order to limit direct exposure to the dust. I wish you luck with your colony. Your formicarium looks amazing!
Here's a guide for K-23 nests for future readers