Blondielovesfish
Kia Ora
Dwarf Puffers are completely freshwater, they can only tolerate low levels of salt and being in brackish lowers their lifespan greatly.
From http/www.seymourfish.com/how-to-care-for-a-dwarf-puffer-fish/
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It’s important to realize that because the dwarf puffers are such a new fish, much of the information about them on the internet is inaccurate at best. No matter what you may read, dwarf puffers only thrive in freshwater, and under no circumstances should they be kept in brackish or salt water tank. Any attempt to keep a dwarf puffer in a brackish aquarium, will result in a severely shortened lifespan.
From http/www.seymourfish.com/how-to-care-for-a-dwarf-puffer-fish/