A 55 dwarf puffer and tetra tank? Aren't dwarf puffers brackish and aggressive, or are you talking about something else?
This is a freshwater puffer (Tetraodon travancoricus), originally from Indian. They are territorial and have these little battles for their area within the tank. Almost looks like a dance, while they square up head-to-tail and circle around, until darting off after each other. They will also tail nip other fish, and it’s the reason why the guppies are no longer sharing a tank with the puffers (as well as the puffers being slow, picky eaters). The tetras, I think, are either too big or too fast for the puffers to bother them. Also great if you want to rid the tank of snails…they suck that escargot right out of the shell. They are a neat little fish with eyes like a chameleon…going in different directions.
Anyway, I’m setting up the 75 right now; getting out my plastic plants (ugh!); and going to push the cycle by seeding the tank with rock from an existing tank. Guppies and goldfish, it will be. I also can’t see loosing any adult guppies to the goldfish. With the buggie eyes and slow swimming ability, can’t see it happening.