That's great, but again that doesn't fix the issue of making the puffer sick and it is only a matter of time before he eats the tetras too. There are tons of feeds on here of people trying the same thing, but within a month the Puffers instincts kick in and boom dead fish. Plus fish store fish generally carry things like ick or some kind of gill issue and need to be quarantined. If they have any sickness it will hurt your puffer rapidly. Generally it's just not worth the risk.