Nice plants! I never seen them before, are they real or fake ? Anyway just a thing, you should remove the stones because the frog will eat everything will move and if another frog move the stones it can get swallowed by the bombina with serious and potentially mortal consequence. If you want to add stones they should be or too big to be swallowed or too small and too roundish to be dangerous. Bombina doesn't require a bottom anyway, but a lot of people including me add it to aesthetic purpose, I've mostly gravel reduced into sand by myself but if you choose it you must be careful because is hard to clean (but bombinae love it). (PS: sand is dangerous for full aquatic frogs and newts)