Just FYI that's not a deepwater japanese toad, it's just a tyree.
It was my understanding that the true Japanese green toadstools had a neon green cap and neon green polyps. I do agree that your polyps are different than a regular tyree so it could be a Japanese variety that is also a slow grower.
Unless you can claim lineage I would just say it's a nice toadstool, but who am I to judge.