Green spotted puffer

Does anyone have any experience/advice for keeping green spotted puffers? I just got my girlfriend a 20 gallon and she decided she wants one. I haven't had any but I was reading up on them and people were saying they do good better in brackish water as they get bigger? Also they said it's good to feed them snails. Any specific type? Any info/advice will be appreciated because I don't think I can talk her out of these.

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