My dwarf puffers love baby pond snails, which you can usually get for free at the fish stores. It's a lot of fun to watch them chase after a falling snail, stare at it confused (probably figuring out the best way to attack), then suddenly go in for the kill. If the snail is too large, they will suck it out of the shell. However, you want snails about the size of the puffer's eyes so they can take the whole thing into their mouth and crush it, which keeps their teeth trimmed. I've heard they also eat ghost shrimp, but I can't seem to find any that are small enough, so my 4 cm shrimpies share the tank with the puffers.
I came home with 5 adorable dwarf puffers to live in my community tank after I was assured by the LFS that they were not only 100% freshwater, but also very friendly. I'd asked because I had just returned a beautiful pictus catfish for harassing my other fish, after I'd been told that it was friendly as well. Of course the second they hit the water they started chasing everyone and I did a little research and discovered that I'd been had: they're cute and tiny but ferocious. I was too embarrassed to bring them back, and my LFS has a policy where they will take "donations" but won't exchange, so I put them in a little bow-front 20 liter tank on my desk. They eat blood worms, love snails and will double their weight twice daily with brine shrimp, which is to say they're a hassle to feed, but the show they put on makes it worth it. I watched them, they were cute, they got fat every time they ate and seemed to get along just fine. Then one day one of them wouldn't eat. After about three days he looked like a little skeleton and the fourth day he was dead. About a month and a half after that the exact same thing happened to another one. With only 3 fish left I watched them very carefully to see what was up. I had been left with 2 bigger fish, with light spots, and one little but very healthy guy with dark spots. From what I read it seemed that I had 2 girls and a boy and things would be alright. Then one of the big ones started chasing and nipping at the little one. I went to my fish store and asked if I should get a fourth fish, a boy, so they could pair up, or maybe bring the small fish in so the last two would be of the same size, or bring in the "aggressor". They assured me that if I gave them the mean fish that my last two puffers would get along famously. Now I have a tank with two tiny fish in it and, of course, the big one, who had been mellow before, now chases the little one around and nips at him constantly. I don't know what to do - I don't really want a tank with only one half-inch fish in it, but I have to break them up or the little one will meet a terrible end. Of course I'm scared that if I get more puffers I'll run into the same hassles but it seems no one has any luck keeping them with any other fish. They're wonderful to watch but it seems like you're either lucky with them or you're not.
I bought three of these little guys to live in my 125 liter tank. At first, they just hid in one part of my tank, beside some plants. Then, about 3 days after I bought them, almost all of my fish had chunks taken out of their fins and tails. It was only one attacking my other fish, but it got my 3 of my 6 tetras, 2 of my female guppies, my female betta, and even my panda cory. I took them out immediately and took them back to the store I bought them from. The guy that worked there was really shocked to hear that one was attacking my fish, because they're supposed to be so peaceful, but as cute as they are, I will not buy anymore.
These fish are very attractive, and have lots of personality. They are also vey fun to watch, as they will be sitting motionless one moment, and zipping around the next, all with seemingly no fin movement. Mine is in a community tank with several other fish, all bigger than him, but he is the boss! I keep him well fed with blood worms and tubifex to keep him from nipping, but he'll still chase away any fish (even dwarf gouramis and rosy barbs) that get too close. I like to add a litle aquarium salt (1 teaspoon per 20 liters), as this seems to keep him healthier. It is also a good addition for the rest of the inhabbitants, as it prevents disease. Overall, a spunky little fish with no problems, as long as they're well fed.
I just purchased 3 mini puffers...and have fed them what the are said to enjoy, yet the still nip at my tetras, algae eaters and spotted cory catfish. I cannot seem to deter them, they are relentless!
We have been keeping 2 of these puffers with 1 oto cat and 4 bumble bee gobies for approximately 6 months now. We started with 4, this very aggressive pair killed the other two off. They are in our experience VERY aggressive with anything else - we've had a few mishaps. They are tons of fun, very entertaining. Ours are in a brackish enviroment. They eat just about anything we offer them. We recommend them for any puffer fish beginner.