If you're looking to expand your fishkeeping hobby beyond the world of freshwater and saltwater aquariums, brackish water might be the unique middle ground you're after. This aquarium type does require a bit more experience, specialised knowledge, and dedicated care, but our guide will help you to get started.
Of course, if you’ve not heard the term before, you might wonder what exactly is brackish water? Don’t worry, we’ll break down everything you need to know about creating and maintaining a brackish water setup, from salinity levels to the ideal tank conditions. Keep reading to find out which fish species thrive in this in-between environment and how you can build a thriving brackish aquarium of your own.
What is brackish water?
Simply put, brackish water is saltier than freshwater yet not quite as salty as seawater. To help give you more context, areas that are typically considered brackish are estuaries where the river meets the sea, mangroves, and coastal lagoons. Basically, any area where fresh water meets seawater.
This salt concentration means that a number of plants and animals can thrive in such conditions. This is great news for experienced fishkeepers, as this means that keeping a brackish tank can allow you to create a more unique environment and keep new aquatic species.
What species are classed as brackish water fish?
There are lots of hardy species that can survive in brackish water. The list is fairly extensive, but to give some examples, it includes the following aquatic species:
- Archerfish
- Indian Mud Moray Eel
- Red Scat
- Mudskipper
- Silver Scat
- Spotted Scat
- Bumblebee Goby
- Dragon Goby
- Mayan Cichlid
- Pufferfish
- Mollies
- Green Chromide
Of course, the list doesn’t just include fish. There are plenty of live plants that will survive and flourish in brackish water, including anubias, red mangrove, java fern, bacopa, cabomba and vallisneria.
How to set up a brackish aquarium
Generally, when looking at the salt concentration for brackish water, you should look to have a concentration between 0.5 to 30 ppt. In relation to an aquarium, this would translate to a specific gravity (SG) between 1.005 and 1.020. Most experienced fishkeepers will know what SG means, but if you’re new to the hobby, specific gravity is a way to measure the relative number of dissolved salts in your aquarium water in comparison to pure water.
The advantage is brackish fish are quite hardy and will not require exact and precise measurements. However, maintaining close to this balance is needed to ensure the well-being of your aquarium's inhabitants. The following tips will help you to set up your tank with ease.
Choosing an aquarium size
Brackish water can be created in any size tank. However, you’ll need to choose an option that can accommodate the species you wish to keep. Brackish fish vary in size, and some species can grow quite large, requiring ample space to thrive. We would recommend aiming for at least a 70 litre tank, but perhaps even larger if you want to keep bigger or more active species.
An open top option like the Oase Scaperline 60 Aquarium can look great and be advantageous when incorporating live plants. However, it’s important to remember that whilst water will evaporate from open tanks, the salt will not, so you’ll need to monitor levels. You’ll also need something to stop jumping fish species (such as a mudskipper) from escaping.
Oase ScaperLine 60 Aquarium £199.99
Step 1: Preparing the aquarium
The first step to installing a brackish tank is to rinse your equipment. Avoid using soap or detergents, as the residues will harm your aquatic life. We would recommend reading our blog ‘how to deep clean a fish tank’ for further tips. After you’ve done this, you can add your substrate, gravel, and decorations such as rocks and driftwood.
We’d also suggest using gravel or fine sand as your substrate, something like the CaribSea Fiji Pink Sand is a great choice.
Caribsea Fiji Pink Sand £36.99
Step 2: Filling the aquarium with water
First, fill the aquarium with dechlorinated freshwater. You can then use a marine salt mix designed for aquariums, adding it to the aquarium with the above SG in mind. We’d recommend dissolving it in a separate container first to ensure that it is more evenly dispersed. This is also essential if you’re transitioning from an existing setup and have aquatic life in the tank already. Additionally, if you are transitioning from a freshwater setup, you should gradually introduce the marine salt to acclimate the water to brackish conditions.
We recommend adding any live plants into your aquarium at this stage as well, because they can help with the cycling process.
Step 3: Setting up equipment
As with any aquarium, you’ll need a filtration system. Make sure that you install a filtration system that can handle brackish water. You’ll also likely need to use a heater to maintain water temperatures between 23°C and 29°C, as well as some marine lighting in your tank.
Because you’ll likely have a larger tank, we’d suggest opting for a filter system such as the Hagen Fluval U2 internal filter - capable of handling tanks from 45-110 litres.
Hagen Fluval U2 Internal Filter - A470 £45.99
Step 4: Cycling the aquarium
Before introducing your fish to their brackish water home, you must establish the nitrogen cycle to build beneficial bacteria that process waste products. This is a process that can take several weeks. To ensure that the waters are suitable, you’ll need to regularly test some specific parameters, including ammonia, nitrite, nitrate levels, and specific gravity, and adjust accordingly using additives.
Step 5: Introducing fish
Gradually introduce your fish to the brackish environment to allow them to acclimate. For example, if you’re starting your tank with freshwater species that can survive in a brackish environment, you should slowly increase the salinity over the course of a few weeks, as this will allow them to begin to adjust to saltier waters without stress.
Of course, as with any tank, you’ll also need to ensure that the species you are choosing to put in your tank will be able to tolerate each other, and you need to be careful not to overcrowd your tank. We have plenty of useful guides on our blog to help you ensure the health of your tank.
Create your brackish aquarium with Abracadabra
Brackish water tanks offer a rewarding challenge for aquarists looking to level up their skills. With the right knowledge, careful planning, and commitment to regular maintenance, you can create a thriving environment for some truly fascinating species that you won’t find in typical freshwater or marine setups.
Whether you're drawn in by the unique mix of conditions or the rare fish that call brackish waters home, we have a wide range of products to help you achieve your dream tank. Browse our marine care collection to get started.