If you don't want to give him brackish water then I would return him. They are native to brackish waters and this should be duplicated in captivity. Puffers on the other hand SHOULD be kept in brackish (esp. Fig 8's and Spot) but they can be kept in freshwater and saltwater. If they are kept in freshwater they require a high pH of at least 7.6. Figs and Spots can be kept in freshwater, brackish, and saltwater but you will see best colors, health, etc in brackish. Why don't you want a brackish tank? Nothing personal just wondering. Brackish has some of the most amazing and oddball fish. Can you find an Anablep Anablep (4-eyed fish) in freshwater or saltwater? Nope! Can you find an Archer that can spit water in order to knock insects off a branch above the water in freshwater or saltwater? Nope! Also can you find a Mudskipper anywhere else other than Brackish? Nope! Just thought I would point out some of the highlights of brackish.