Yeah, I'm not a big fan of any kind of Puffer with other fish. When I had Dwarves (aka Pea Puffers) with other fish they tail nipped.

If you are having luck (because, it IS luck ) with him in the setup you have him in now, then I'd suggest you leave things as they are, and monitor the tank closely.

My general advice is that Puffers are Predators and as such rarely make good tankmates, and this is particularly so with different species.