Brackish nano fish/inverts?

[LordJoshaeus]

I am considering setting up a 10 gallon brackish (about 20 ppt) setup for my Pseudomugil cyanodorsalis instead of putting them into a reef tank (I will most likely still set up the reef tank, though...I just might not put the rainbow fish in it). Is there anything - fish, inverts, or even macroalgae - I could keep them with in such quarters? Opae ula shrimp came to mind, but I am struggling to come up with much else. Thank you :)