“What is brackish water?” you may ask. Brackish water aquarium is a unique and special type of aquarium as it is neither regular freshwater nor saltwater. Simply put, this is a mix of saltwater and freshwater ecosystems in an enclosure.
In nature, brackish water forms when freshwater meets with seawater. Thus, creating habitats that are a mix of saltwater and freshwater. Brackish water occurs in coastal streams, estuaries, and mangroves.
Before setting up a brackish water aquarium, you should learn about the features and requirements as it is not the same as a saltwater aquarium but very simple and not too different than a freshwater aquarium. You will need the following equipment for brackish water setup:
- tank,
- filter,
- lighting system,
- heater (optional),
- air pump,
- substrate,
- marine salt mix,
- RO water,
- hydrometer or refractometer,
- test kit.
This article explores a step-by-step process of setting up a typical brackish water tank.
Basics: Brackish Water Aquarium Requirements
It is essential to understand that brackish water has more salt than ordinary freshwater; however, it is not as salty as seawater.
For comparison, the reef or saltwater tank has a salinity level of around 35 ppt or 1.026 specific gravity (SG); meanwhile, freshwater is around 1.000 SG (less than 0.5 ppt).
As we can see, brackish water is a pretty broad term. Technically, we can use this term to describe any water whose salinity is between that of fresh and marine water.
In reality, though, aquarists usually do not work with that range of salinity. The main problem is that there are not many Euryhaline animals (fish, shrimp, crabs, snails, etc.) and aquatic plants that can tolerate such fluctuations.
| That is why, in the aquarium hobby, the salinity of brackish water environments often ranges between 0.5 ppt (SG = 1.0004) and 12 ppt (SG = 1.010). |
As always, our goal is to replicate this in a brackish water aquarium. Also, note that brackish water also has a higher PH and alkalinity than typical freshwater.
Other brackish water requirements include
- pH: 7.5 – 8.5
- Alkalinity: 10 — 18 KH
- Temperature: 72 – 82 °F (22 – 27 °C)
- Nitrate: < 30 ppm
- Nitrite: 0 ppm
- Ammonia: 0 ppm
Step 1: Planning (Tank Size, Location, Budget, etc.)
This is probably the most important step because it can help you to save nerves, time, and money.
You need to understand the size of the tank you want – consider your budget, type of materials (glass or acrylic), the space and place available in your home, size of fish and inverts you intend to keep, temperature, etc.
All these factors will help you make a proper decision. Here are some useful tips.
1.1. Tank Size
In setting up a brackish water aquarium, there are no limits. Generally, the only deciding factor here is the size of the animals and plants to be housed in the aquarium.
For beginners, I’d recommend starting with at least 10-gallon tanks (40 liters) and there are many reasons for that:
- It is easier to maintain water quality in bigger tanks because the larger water volume dilutes the waste products way better.
- It can be very difficult to create a proper hardscape in small tanks.
- It is easy to overstock in small tanks. In many cases, it may cause aggressive behavior.
- In a small tank, it can be difficult to create a natural environment in which your animals will thrive.
Basically, the tank should provide enough room for increased activity (swimming or crawling space) for the fish and invertebrates.
Remember, the bigger the tank, the easier it will be to look after.
1.2. Shape of the Tank. Length or Height
Once again, the shape of the tank should depend on the species you are planning to keep.
For example, invertebrates (shrimp, crabs, lobsters, etc.) prefer long tanks to tall ones. Unlike fish, they need mostly a place to crawl from side to side, not up and down.
1.3. Location of the Tank
A good location is crucial. Do not place the tank near air vents, doors, and windows that get direct sunlight.
A good spot should provide easy access to the tank, alongside the plumbing and other components. It also should be near an electrical outlet and in an area that is able to tolerate a water spill.
For more information, you can also read “7 Tips for Shrimp and Fish Tank Location”.
Step 2: Cleaning, and Testing the Tank
We need to clean and test any tank before using it. Yes, even if it is brand new! There is nothing worse than finding out that the tank is leaking.
2.1. Cleaning
We can use bleach, vinegar, or hydrogen peroxide for that.
- Spray the chemical on the walls.
- Let it sit for 10 – 20 minutes.
- Wash it off properly (repeat it at least 2 – 3 times to remove everything). DO NOT use soap, it can leave a residue in the tank and we don’t want that.
Related article:
2.2. Leaking Test
Do that to be sure that the seams of the tank are not damaged.
- Put some paper underneath the tank.
- Fill it with water.
- Wait for 1 day.
If you do not see any wet spots on the paper, the tank is safe to use and you are good to go.
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Step 3: Substrate
3.1. Choosing Substrate
When choosing the type of substrate to be used in the brackish tank, it is advisable to mimic the natural brackish environment as much as possible.
Important: Substrate is not only a decorative piece, it also serves as part of your biological filter as it provides a viable medium for nitrifying bacteria to colonize, and harbors many micro fauna.
Crushed coral and aragonite sand are pretty popular amongst brackish water aquarists because it helps to maintain the water hardness and pH levels.
Sand or plain gravel are good substrate options as well. These two materials can be mixed and used in the brackish water aquarium.
Note: Soil is not recommended for brackish water tank setups as it tends to lower pH.
3.2. Preparing Substrate
Do not simply dump it right away!
Sand and gravel often contain lots of debris (dust and dirt). So, if you forget to rinse it, your tank can turn into an uninhabitable cloudy mess.
Note: Even so-called “pre-rinsed” or “pre-cleaned” substrates can contain dust, debris, grit, or other residues in the bags from the workshop they were packaged in.
How to Prepare Sand for Brackish Tank
- Place it into a bucket and spray the sand with a hose.
- The excess water will run out of the bucket and the water will be cloudy and dirty initially.
- Keep rinsing. You will notice that the water will run clearer.
- If you think that sand is clean enough – rinse it again for a few more minutes!
How to Prepare Gravel for Brackish Tank
- Put the gravel into the bucket.
- Fill the bucket with tap water. The water should completely cover the gravel.
- Stir and move the gravel around (use a stick if necessary).
- Leave it in the bucket for 5 – 10 minutes. It will soften up any dust and debris that may be on the gravel.
- Stir and move the gravel around one more time.
3.3. Adding Substrate to the Tank
You will need to spread and maintain a thin substrate layer, ideally about 1 – 2 inches (2.5 – 5 cm) at the bottom of the brackish aquarium.
Make sure that the aquarium substrate is well-distributed and level at all sides. You may also place smooth pebbles, stones, twigs, tree roots, and driftwood as seen in natural brackish environments.
To improve visual perception, aquarists often create a little slant to give the aquarium a little more depth.
To achieve this result, make it a little higher in the back and lower in the front. Because of this trick, the size of your tank will look larger.
Step 4: Brackish Water
It is crucial to use the marine salt mix as against regular aquarium salt. I repeat, never use freshwater aquarium salt to make brackish water.
Sea salt will replicate natural brackish chemistry, and it should be mixed with RO/DI water in the right amounts to attain the desired salinity.
Good sea salt brands include (link to Amazon):
- Instant Ocean & Reef Crystals Reef Salt (probably the most popular choice),
- Seachem Marine Reef Salt,
- Kent Sea Salt,
- Coralife Marine Salt and
- Tropic Marin Bio-Actif Sea Salt.
4.1. Preparing Brackish Water
As I have already mentioned, the ideal salinity for this kind of aquarium ranges from 1.005 to 1.010 SG (up to 12 ppt).
To achieve this, we usually should add about ⅛ cups of salt for each gallon of fresh water in a plastic bucket. Use a good hydrometer or refractometer (link to Amazon) to take accurate measurements.
- Stir the water properly.
- Bring the water to the desired temperature.
- Let it sit for about 20 – 30 minutes.
- Stir again to ensure that the salt is entirely dissolved and evenly distributed.
- If the salinity level is high, add more freshwater, and if it is too low, add more marine salt mix.
Tips: Make sure to calibrate the refractometer for the first time and after using it a few times, use a calibrating solution. To ensure a true reading of the salinity of the water, do not forget to wash the refractometer with RO/DI water before and after using it.
4.2. Adding Brackish Water
The water is now ready to be transferred into the brackish tank — place a bowl inversely on the substrate and pour the water on its surface slowly to avoid dislodging the substrate bed.
Is it possible to use tap water for a brackish tank?
Yes, it is possible but not recommended!
The main problem with tap water is that it contains impurities (phosphates, nitrates, silicates, iron, copper, etc.) that are harmful and often lead to outbreaks of nuisance algae and dead animals.
In addition, because of impurities, it will be hard to create a proper mix of tap water with marine salts.
As we can see, the risk is huge and the choice is yours.
Step 5: Aquarium Equipment
This includes the addition of an efficient:
- lighting system,
- filtration,
- heater,
- air pump or powerhead.
5.1. Lighting System
Any high-quality lighting system that would make the tank come to life and enhance the aesthetical appeal of the interior is ideal.
But if you plan on adding picky animals or demanding live plants into the aquarium, consider their lighting needs before acquiring aquarium lights.
Lighting sources for the tanks include Light-emitting diode, fluorescent lamps, and T5/T8 lighting. If plants are added to the tank, ensure that the light is safe and its output is sufficient to promote their growth, coloration, and development.
Read more about it in my article “Advanced Guide to Planted Tank Lighting”.
5.2. Filtration
Filtration is critical in brackish water tanks as it is in other aquarium setups. It will keep your tank clean, and maintain the nitrogen cycle. Thus, an efficient filter unit needs to be present to handle the filtration needs of the brackish water tank.
Viable options include:
- Hang-on-back (HOB) filter,
- Sponge filter,
- Corner filter,
- Under gravel filter,
- Trickle filter
- Canister filter.
So, what filter is the best for the brackish tank setup? It can be really confusing, especially, if you are new to the aquarium hobby.
In my opinion, considering the specific needs of this tank setup, such as: salinity, ease of use, safety, and budget – I would recommend taking a look at canister filters or hanging on the back filters.
However, a canister filter would do an excellent job, especially if you have a sizeable brackish water aquarium with a high bioload.
Tip: Always opt for a more powerful one. For example, if you have a 15-gallon (60 liters) tank, choose the filter, which is rated for at least 20 gallons (80 liters). The difference in money is minimal but the benefit is huge!
Some examples (links to Amazon):
Related article:
5.3. Heater
Important: Unlike filters, only choose the heater appropriate for your tank size. If the heater is larger than what your tank actually requires, it may lead to overheating and ultimately – “cooking” your animals.
I strongly recommend using only adjustable heaters. It is just more practical. If you have a preset heater in your tank and it’s not heating it to the proper temperature, then there’s no way of adjusting it if it’s preset.
Also, make sure that the heater can be used in fresh and saltwater aquariums.
Do your research regarding the animal or plant species you are planning to keep! It is quite possible that you will not need the heater.
For example, on this site you will find that many invertebrates prefer the temperature in the range of 20 – 24 °C (68 – 74 °F). Basically, we can say that they do not need a heater.
Nonetheless, keep in mind that, it only takes one big fluctuation in temperature that can potentially cause your animals to suffer from temperature shock.
Related article:
Example (links to Amazon):
5.4. Air pump and Powerheads
Install your air pump or powerhead to provide oxygen or sufficient flow and water movement in the tank.
There are manufacturer instructions on how to install these types of equipment.
Example (links to Amazon):
Step 6: Cycling the Brackish Water Aquarium
Before introducing fish and other aquatic critters into your brackish water tank, it is essential for the tank to successfully commence and complete its nitrogen cycle, which often takes several weeks.
The end of the cycling process makes the aquarium safe and stable for the addition of aquarium fauna.
There will be high ammonia and nitrate at the early cycling phase in the aquarium water.
The essence of cycling is to convert ammonia into nitrite and nitrite into less toxic nitrate.
This happens after beneficial bacteria has formed in the tank, and within 4-6 weeks, the bacteria break down harmful ammonia and nitrite into nitrate. Do not change your filter during this time.
This step is a vital one in setting up a successful brackish water aquarium.
Test for ammonia, nitrite, and nitrate every few days and record the results in a log. Patience is the single most important here. The tank has properly cycled when the ammonia and nitrite levels are undetectable, i.e. 0 ppm.
Suppose this process takes a lot of time; in that case, live bacteria supplements like Tetra SafeStart, API QuickStart, and Nutrafin Cycle may be added to increase the bacterial populations, hastening the cycle rapidly.
Step 7: Choosing Your Brackish Water Animals
Below you will see some examples of fish and invertebrates that can tolerate different levels of salinity. However, it does not mean that you can switch them from freshwater to brackish water in a matter of hours!
We have to understand that once they adapt to live in brackish water as juveniles or adults it may be hard to acclimate them to freshwater (and vise versa) without adverse effects (like decreased lifespan, extra sensitivity, etc.).
Acclimation from freshwater to brackish or from brackish to freshwater should take days or weeks!
7.1. Examples of Invert Species for Brackish Water
| Crab species | Salinity Tolerance | |
| 1. | Red claw crab | 1.002-1.010 (as adults) 1.015- 1.0188 (as larvae) |
| 2. | Fiddles crabs | 1.005-1.021 |
| 3. | Ninja shrimp | 1.000-1.005 (as adults) 1.0128- 1.0188 (as larvae) |
| 4. | Red Nose shrimp | 1.000-1.0113 |
| 5. | Opae Ula shrimp | 1.008 – 1.018 |
7.2. Examples of Snail Species for Brackish Water
| Snail species | Salinity Tolerance | |
| 1. | Chopstick snails | 1.002-1.010 |
| 2. | Horned Nerite snails | 1.0038-1.0075 (as larvae) |
| 3. | Nerite snails | 1.0038-1.0075 (as larvae) |
| 4. | Hairy snails | 1.0038-1.0075 |
| 5. | Black Devil snails | 1.002–1.025 |
7.3. Examples of Fish Species for Brackish Water
Not every type of fish can adapt in a brackish water aquarium setting. However, some popular freshwater fish, e.g. Guppies and Mollies (Poecilia sp.), can also tolerate and adapt to low brackish water, even though they don’t actually need salt in their water.
Common brackish water fish species include:
| Fish Species for Brackish Water | Salinity Tolerance | |
| 6. | Knight Goby (Stigmatogobius sadanundio | 1.001-1.005 |
| 7. | Figure-eight Puffer (Dichotomyctere ocellatus) | 1.000-1.005 |
| 8. | Skunk Goby (Redigobius balteaus) | 1.002-1.008 |
| 9. | Spotted Puffer (Dichotomyctere nigroviridis) | 1.005-1.020 |
| 10. | Bumblebee Gobies (Brachygobius spp.) | 1.002-1.006 |
| 11. | Colombian Shark Catfish (Ariopsis seemanni) | 1.010-1.020 |
| 12. | Monodactylus argenteus | 1.005-1.025 |
| 13. | Golden Puffer (Auriglobus modestus) | 1.005-1.010 |
| 14. | Orange Chromide (Etroplus maculatus) | 1.005-1.010 |
| 15. | Mudskippers (Periophthalmus spp.) | 1.003-1.015 |
Important: Before you buy a new fish or invertebrate, make sure to research and learn about the salinities they can tolerate and their temperament, behavior, feeding, and temperature needs.
Choosing Your Brackish Water Plants
It is no secret that plants add a lot of life and vitality to the aquarium, providing an almost natural habitat for the fishes by making their life super comfy and enjoyable.
Some easy-to-grow brackish water plants include:
| Plant Species for Brackish Water | Optimal salinity levels | |
| 1 | Marimo moss balls (Aegagropila linnaei) | up to 1.0045 SG |
| 2 | Anubias (Anubias spp.) | up to 1.005 SG |
| 3 | Java fern (Microsorum pteropus) | up to 1.0075 SG |
| 4 | Duckweed (Lemna minor) | up to 1.005–1.007 SG |
| 5 | Vallisneria sp.(Americana and spiralis) | up to 1.0068 SG |
| 6 | Dwarf Water Lettuce (Pistia stratiotes) | up to 1.0019 SG |
Make sure to acclimatise these plants slowly to brackish water before adding them into the brackish water aquarium. Failure to do this may cause the live plants to melt in the tank.
Related article:
Introducing Fish to the Brackish Water Aquarium
- Test the water parameters and ensure they are ideal after the cycling process.
- Here, it is advisable to introduce one fish at first and see how it adapts.
- After some time, test the aquarium water again, then add a few more gradually.
- Adding too many fish at a time can cause the brackish water tank to cycle all over again due to the increased release of toxic waste (ammonia) in the water.
Maintenance
Brackish water tanks require routine maintenance to keep the ecosystem stable and healthy for the aquarium inhabitants.
Maintenance takes the form of changing the water regularly, cleaning the filter and tank, wiping and testing equipment, and engaging in frequent water testing to ensure the appropriateness of the water parameters, etc.
Tank cleaning involves scrubbing/wiping the aquarium walls to remove algae, cleaning the ornaments, changing the filter media, and vacuuming the substrate regularly. Also, change the aquarium water from time to time; a 15% water change every week is appropriate. This activity would help maintain excellent water quality and keep the nitrate at the ideal levels.
Remember to always mix the aquarium water externally before adding it into the aquarium. Never add salt mix directly into the aquarium; doing so will harm your critters.
Usually, water will evaporate from the tank, thereby increasing the salt concentration in the aquarium. So top up the loss with freshwater, and endeavor to test the water from time to time using a refractometer or hydrometer.
When the salinity level drops or elevates considerably, you risk losing your aquarium animals and live plants. That said, you should strive to keep the water salinity at the correct levels at all times.
Is it Possible to Transform the Tank from Freshwater to Brackish?
The short answer is yes.
The most important thing here is that this process should not be rushed. If you do it slowly (over a period of at least several weeks) it will not hurt the beneficial bacteria and disrupt the nitrogen cycle.
- Instead of freshwater, use brackish water during regular water changes (15-25%).
- The changes should be slow. For example, at first, your tank water needs to become 1.003 (or 5 ppt). After that, you can increase the salinity to 1.006 (or 8 ppt), etc.
Should I Use Freshwater or Saltwater Test Kit for Brackish Tank?
Unfortunately, there are no test kits on the market which were designed specifically for brackish water tanks.
Therefore, the answer will depend on the salinity level.
For example, for low to mid salinity levels, API customer service suggested using freshwater test kits for brackish tanks as the salt water colors do not show the correct readings as the freshwater color cards do.
However, if salinity is more than 1.015 SG (or 20 ppt) then the salinity test kit can be more precise.
In Conclusion
If you have a freshwater aquarium and fancy a new challenge — consider keeping a brackish water aquarium. This aquarium setup offers a unique environment suitable for animal and plant species with a reasonable degree of salt tolerance.
I hope this guide provides you with all the vital information required to successfully set up and maintain a brackish water aquarium in your home or office.