That small? Dwarf Puffers must be a lot smaller and more accepting of small tanks than I knew. I may look into these myself. Sort of a midway step on my way to maintaining saltwater.
They only get to be about an inch long. And I'm just assuming at this point, but if anyone told you dwarf puffers are brackish, they were wrong. DP's are 100% freshwater.
I've heard some are Brackish but I didn't know there were Freshwater. I did some looking on them and found nearly all of the ones that came up are fresh.
Be sure to get a good ID on the puffers. Unfortunately there seems to be very few lfs that are knowledgable about puffers. I have talked to folks that bought "Dwarf puffers" only to find out after they had them for a little while that they were in fact Green Spotted puffers and needed to be moved to BW as they started to mature.
Check the list at the top of this section for a starting list of FW/BW puffers