Dwarf Puffers in a 10 gallon Hex?

You would be fine with maybe 3 of them in there. 4 might be okay as long as you could provide enough food, keep the tank super clean and provided hiding places and line of sight blocks.
 
Yes, puffers do not do well at all in bad water conditons. Also make sure they are plump when you buy them. If they have skinny bodies they will just end up dying.

And make sure to have plenty of live food on hand, at least for the first 6 months or so as they won't eat anything else. And they go through snails really fast, so a separate snail tank is always a good idea. Brine Shrimp and Mosquito Larva are also good.
 
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