[Chaos553]

I've been thinking about setting up an old 10g tank to put my guppies from my 20g into so I could change my 20g into a brackish tank. For starters, I was wondering what a need specifically to start out a brackish tank. I'm aware that I need marine salt and a hydrometer, but are there any specific parameters I need to meet? Also, are there any fish small enough to fit in this tank? I was thinking about going gobies but im still unsure on the idea since it could be a bad one. Help would be awesome.