Calling all fish experts?

I wanna say thanks in advance for any responses I get. This might be a stupid question but I am planning on setting up a dwarf puffer tank (10 gal) and I know they thrive in brackish water and I was wondering if there is an easy way to set up a brackish tank. Also I plan to use a fine substrate, maybe something like sand and I would like to put a Dragon fish in with it too because I know they like to burrow and also like brackish water but I don't know if the puffers will har it due to their aggressive nature. I have a solid general knowledge of everything I want to do and how to care for the fish it's mainly just setting up the tank and the chemistry between the fish I want to know about.