A GSP is a fish that needs a mid to high brackish environment. Some people even keep them in full seawater. Thus, you need a mid to high brackish tank or even marine. This should really be in the brackish section though, since this puffer is brackish. Does this answer your question?
the only thing extra you would need would be instant ocean salt, a bucket to mix it in, and a hydrometer/refractometer to measure the levels of salt. In most cases they have a tank dedicated to just them, quite sensibly.