different brackish fish thrive under different water conditions, so it all depends on what individual fish. monos would be nice, check out some monodactylus argentus for a bit more color as opposed to the sebaes. the snowflakes they sell as freshwater do much better in extremely brackish water and eventually a marine conversion, same thing with fish like scats. You could do a jade goby, an archerfish, maybe some decent sized red or green chromides, even some dragon gobies with ample hiding spaces. None however are that colorful, but brackish fish make up in uniquity for what they lack in looks. There are also much more unique brackish fish out there but they would require a specialized tank for the most part. Good luck with your hunt.