Brackish Fish & Aquariums
Brackish aquariums recreate estuaries and coastal lagoons where fresh and saltwater mix. They are often simpler than full marine systems, but they still demand consistent salinity and careful species selection.
Getting started with brackish tanks
Brackish success is mostly about matching the fish you want to keep with a stable target salinity. Many brackish species are hardy, but they do poorly when salinity swings or when they are kept in the wrong range.
- 1. Pick species first, then choose a target salinity that fits them.
- 2. Mix saltwater correctly and measure salinity with a reliable refractometer.
- 3. Cycle the tank fully before adding fish.
- 4. Acclimate slowly when changing salinity.
- 5. Keep it stable: top off evaporation and avoid sudden changes.
What you'll typically need
Brackish tanks are about routine and measurement, not complicated gear.
- Tank + heater + filter
- Marine salt mix + mixing container
- Refractometer and a basic test kit
- Top-off plan to manage evaporation
What is brackish fishkeeping?
Brackish fishkeeping uses slightly salty water (between freshwater and seawater). Many brackish species come from estuaries where salinity changes with tides and rainfall, but they still thrive best when your aquarium stays consistent.
The key difference is that you are managing both water quality and salinity. If you measure accurately and keep changes gradual, brackish tanks can be very stable and beginner-friendly.
What you'll focus on
- Stable salinity and temperature
- Gradual acclimation when making changes
- Species choice based on adult size and temperament
- Simple routines for testing and water changes
The 4 fundamentals (and why they matter)
Brackish tanks fail when salinity is guessed instead of measured, or when changes happen too fast. Aim for a steady target and keep your routine consistent.
- Cycle first
- A stable biofilter prevents ammonia and nitrite spikes, regardless of salinity.
- Measure salinity
- Pick a target range and measure it reliably. Top off evaporation with fresh water to avoid salinity creep.
- Right equipment
- Stable temperature and strong filtration make brackish tanks predictable and easy to maintain.
- Stock smart
- Many brackish species get large or boisterous. Plan for adult size and temperament.
Acclimation matters
When moving fish between salinities, changes must be gradual. Even hardy species can struggle if salinity shifts quickly.
- Adjust salinity slowly over days, not minutes
- Match temperature and reduce stress during transfers
- Stability after changes beats frequent tweaks
Common mistakes (easy to avoid)
- Guessing salinity instead of measuring it
- Using saltwater for top off (it raises salinity)
- Keeping a species in the wrong salinity range
- Overstocking fish that grow large
- Making rapid changes to fix minor issues
New to brackish fishkeeping?
Brackish tanks can be a great step up from freshwater. Measure your salinity, keep it stable, and choose species that match your target.
- Measure: use a refractometer, not guesswork.
- Top off: evaporation changes salinity.
- Pick fish first: salinity follows the livestock.
Explore Brackish Topics
Brackish tanks sit between freshwater and marine. Start with the right salinity and species, then keep it stable.
