Brine Shrimp? Adults get to maybe 1/8". They are food, nothing more, and can only live for more than a few hours in heavily salted water.
If you intended to ask about Ghost Shrimp, which is what I actually suspect, adults get to around 1", females possibly as large as 1.5". They do not need brackish water, they are a true freshwater shrimp, and usually do great in a community tank. They are harmless to the fish, so the only real issue is whether or not the fish pick on them. If they are getting picked on constantly they will eventually just hide and only come out at night, otherwise they will be out all the time and they are fascinating to watch.