Glossary · 💧 Water & chemistry
Brackish water
Brackish water is water with a low, deliberate amount of salt — between fresh and marine — needed by a handful of specialist fish and by the larvae of some snails and shrimp, but not by ordinary community fish.
It is a common myth that adding "aquarium salt" benefits all freshwater fish; most do not need it and some (like many catfish) dislike it. True brackish keeping is a niche with its own species.
The practical takeaway for beginners: nerite snails and amano shrimp will not overrun your tank precisely because their young need brackish or marine water to develop, which a freshwater tank cannot provide.