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I had experience with a similar species - congo puffer.
Pignose are lurkers and don't really move around. Once these puffs get used to the keeper, then they will swim up to the glass. Some are lazy and keep themselves buried until you bring the food up to their face.
Sand bed is apx 3" there is a royal pleco in there about the length of a dollar bill and a tiny one about 3" I wouldn't want them hurt. As long as they would be ok I wasn't one. They're truly fresh right not brackish.