I have the same problem. I used to have 4 little dwarf puffers but moved them to a new tank. I now have 3 empty 10g tanks. And I was gonna make a thread asking everyone here what I can put in them. I already have tanks with neon tetras, platy's, and other colorful small fish. I have been thinking about this all morning....wondering what I can do with my empty tanks. Hmmm...do you have any neon tetras or small danios? I have one tank with a school of neon tetras, and a school of zebra danios, some blue mystery snails, 2 rubberlip pleco's, and 3 guppies. It's my pretty peaceful tank...maybe something like that could work?