Hello, This is a real late post, but.. I'm no expert,but... I'd put each of these in their own tank - at least a 29G. Landscape like a jungle. enough so they can meander in and out and around the plants, .ie can't swim in a straight line. Get some driftwood and caves in there for hiding places. I wouldn't have turbulance from filter returns. I feel these guys need a maximum of space and no other Puffers, I think very possible you'll find they will compete aggresively for food with a Puffer tankmate. As for food I find my Puffers will ONLY eat live food. They've gotten to the point that they will only eat either Pond or Ramshorn snails. One will eat both and one will only eat Ramshorn. Getting complicated, time comsuming, etc yet? And what about snail volume? I go through well over 100 snails per week. I only have 2 Figure 8 Puffers. One is about 3 inches long and one is about 2. Water cleanliness and filter cleanliness is absolutely a weekly must. Maybe your Puffers will eat an easier food to come by. Hope so, it's a shame to watch one's pets languish just because the pet store you got them from was too irresponsible to tell you all these things I'm now telling you. Like I said, I'm no expert, most of what know was trial and error, pet shops are absolutely no help!!! You can read about them on enternet. Good Luck!!!