I get commissions for purchases made through links in this post. Learn more.

How to make Brackish Water for Aquarium

Getting the water chemistry in your tank right is one of the fundamentals of good aquarium keeping. If the basic chemistry of the water is not right, then it doesn’t matter what fancy filtration equipment you install, or what expensive fish food you feed them, your fish simply will not thrive.

Good water chemistry means mimicking the native environment of your aquatic species, to ensure they can remain happy, healthy and strong, for long years to come.

Of course, there are many elements to getting your water chemistry right. For instance, you need to keep an eye on the water hardness, to ensure the level of dissolved minerals is in the right range.

You also need to ensure the correct pH level is maintained, to ensure the water does not become too acidic or too alkaline.

You also need to monitor the level of substances such as ammonia, nitrates and phosphates, since these can have knock on health effects if they get out of hand.

All of these levels have complex inter dependencies as well, which makes it even more confusing.

As well as the above factors, one thing you have to consider is the salinity of the water, since some fish will only survive in brackish water.

If you’ve never heard this term before then don’t fear, as we guide you through the ins and outs of how to make brackish water for aquarium.

What is brackish water?

Before contemplating making your tank into a brackish water paradise, you should first understand the fundamentals of what exactly brackish water is.

Essentially, brackish water is water which is in between freshwater and saltwater in terms of its salinity (i.e. the level of dissolved salt). This means that it is more salty than freshwater, but less salty than pure saltwater.

This kind of water is often found at places where great bodies of saltwater and freshwater mix and churn, such as in the estuaries of great rivers. Many species have evolved to live specifically in these regions.

Brackish water is also found in mangrove swamps, where the level of water ebbs and flows with the receding tide, and even in some bays and brackish seas.

It is also commonly created as a result of big human civil engineering involvement, such as in the construction of dykes and dams, and as a result of the salinity gradient power process, where energy is harvested from separation of saltwater.

Brackish is a term used to denote a wide range of salinity levels, and specific definitions may very regionally. Generally though, it refers to the middle of the spectrum between freshwater and saltwater.

How do you identify brackish water?

As eluded to earlier, brackish water is water which falls within a specific salinity range. Obviously, you don’t want to go around testing the salt levels of waters by tasting them, so there must be a more scientific way.

Thankfully there is. Salinity is easily measured using an electronic probe attached to a meter. This utilizes the conductivity of saltwater to provide a reading. It operates on the principle that saltwater is more conductive than pure, distilled water, and passes a small current through the water.

The general units used to measure the brackish nature of water is in grams of salt per liter of water.

Generally, brackish water contains between 0.5 and 30 g of salt per liter. This could also be expressed in terms of parts per thousand. Usually, a hydrometer in tanks is a simply way of measuring the salinity.

The alternative way of indicating how brackish or otherwise your water is, is to refer to the specific gravity of the water. The same volume of saltwater is heavier than an equivalent volume of freshwater.

The specific gravity of brackish water is between 1.0004 and 1.0226, which you could measure with a precise electronic balance.

These units and methods are important to understand so you can quantify the salinity of your tank and validate that you have actually produced brackish water afterwards.

Why would you want brackish water?

Video: “ALL or Nothing on a Brackish Water Tank”

This is an important question to ask yourself before you go to the trouble of making your tank into a brackish water tank. You need to consider your own personal circumstances to assess whether it is worth it for you.

Of course, it is true that many species of fish (and aquatic plants) will do better in brackish water, but many other types, in particular tropical species, will not do well. You need to consider the long-term knock-on impacts on their health and general well-being.

Every species will react differently so you need to ensure you have made provision for all your fish, especially since this transformation would take quite a lot of effort to reverse.

Species that are best suited to a brackish environment

There are a lot of species that are best suited to a brackish environment. For example, bumblebee gobies and black mollies are found to thrive in the moderately saline waters and they will hence show more vitality and vigor. Also, archerfish and flatfish are generally traded as brackish water fish.

However, many of the fish traded as such may actually thrive in freshwater environments as well. Remember, if in doubt, consult with a more experienced hobbyist.

There are some types of fish that are generally thought of as freshwater species, but are actually native to brackish waters.

For example, the Florida flagfish and certain types of colorful cichlids, although typically kept in freshwater aquariums, may actually display more natural behaviors and thrive better in brackish aquariums.

One other major advantage of owning a brackish water aquarium is that the fish kept in it are usually of a hardy variety that is not as susceptible to damage due to changes in pH or water quality.

That is because, living in tidal regions as they often do, they have great adaptability and have become somewhat used to sudden swings in pH or water hardness level.

This can be a blessing for the tank owner, as they can relax the pH control somewhat, often leading to a more natural cycle.

How to make Brackish Water?

If you have your heart set on setting up a brackish water tank, then the process to follow is simple enough. In many respects it is like a normal freshwater tank, and it will require you to take the same precautions for lighting and size, as well as making sure you have adequate mechanical, biological and chemical filtration in place.

This should help keep your tank clean and clear, ward off any pernicious algae, and maintain a healthy balance in the artificial ecosystem.

The particulars for a brackish tank is obviously the need to introduce salt into the equation. It is very important to consider the type of salt you are using, as not all salts are the same, and unfortunately ordinary table salt will not suffice. It contains too much excess silicates and iodides.

Usually it is best to use a marine salt mix instead of aquarium salt, and table salt is out of the question. A few tablespoons of marine salt mix should provide all the magnesium, sodium and calcium salts to transform your tank into a brackish water safe haven.

The Step by Step Process

The other particulars of a brackish water tank is that it should have a pH level between 7.2 to 8.5 and the temperatures (for most species) should be kept between 25 and 30 degrees Celsius.

Obviously, you should check that this is suitable for all species of fish you plan to keep in the tank.

The process for how to make brackish water is actually very simple, but to get the salinity levels spot on a certain level of precision is needed.

1Firstly, you should fill a bucket with the water you plan to use, which for most purposes will be tap water (assuming that the hardness and pH levels are appropriate).
2Next you should add a heater to bring the water up to the same temperature that you plan on keeping it at in the tank. The reason for this step is that the water will expand when it heats up, which obviously means that the salinity (mg per L) will drop. This means it’s super important to measure the salinity at a constant reference temperature all the time.
3Anyways, once the water is at temperature, you should add your salt. The amount you add depends on exactly how brackish you want your tank to be, and how much water you have. Generally, it is recommended to add approximately 10 grams of salt for every liter of water.
4Once you’ve added the salt, give the water a stir to help homogenize the solution. Then you wait. Allow at least a half an hour to ensure all the salt has dissolved, then stir the water once again.
5Finally, you can start filling the tank. As you do, use a hydrometer or electric probe to keep a constant eye on the specific gravity/salinity levels, and top up as required. That’s the easy step by step guide for how to make brackish water.

Adding Fish

No matter how eager you are, it’s important not to add your fish straight away. You should leave at least a week to allow the nitrogen cycle to flush through, which will help ensure all the dissolved substance levels will have stabilized and some beneficial bacteria will have made their home there, ready to churn through some fish waste!

Note, if you are transferring your existing fish from a freshwater tank to a brackish water tank, then this is a delicate process which should be done over a longer timescale. You need to give your fish a chance to adapt to the new environment and different water chemistry, or else you risk having a negative impact on their health.

You can still use the same recipe for brackish water given above, but simple replacing about 20% of your existing freshwater with the brackish water every week. This will gradually increase the specific gravity of the water, and will avoid any of the nasty shocks that can induce such negative impacts.

What else to add


Video: “Setting A Brackish Water Planted Tank”

Once you have the brackish water in place, you may be eagerly looking for some other ways to adorn your new brackish fish tank.

Well unfortunately, unlike freshwater tanks, your options are somewhat limited. It so happens that most aquatic plants and salt are natural enemies, so they simply will not survive in such a salt heavy environment.

But this doesn’t mean that your brackish aquarium has to be sparse and boring. In fact, it is often good to add some ornaments to your tank to help stimulate the inhabitants, and make it more aesthetically pleasing.

One of the rare exceptions to the rule that plants don’t grow in brackish water is the mangrove.

These small trees or shrubs are native to these waters and some nice mangroves can really complete a brackish water aquarium. There are many other types of realistic looking natural or artificial driftwood. As well as adding some much-needed variety to a tank, these can have the added benefit of softening the water in many cases, by releasing tannins into the water.

Many fish will feel more at home swimming among roots and driftwood as well, as it is not unlike their native swamp waters.

A certain amount of algae growth should be encouraged in brackish water aquariums, such as by providing plenty of sunlight.

This is because many brackish water fish are natural algae eaters, and will happily pick them from the tank floor.


Brackish water tanks are become more and more popular within the aquarium community every year. They represent the natural midpoint between freshwater and saltwater setups, and are attractive to anybody looking to advance their hobby to the next level.

Making the transition can be a bit daunting at first, but once you break it down, the process of how to make brackish water is really very simple.

Using the right type of salt is crucial, and understanding how salinity is measured, as well as the types of fish that are suitable for these tanks, is also extremely important.

If you are looking to transfer fish over from a freshwater setup, then remember to do so carefully and slowly, to avoid any sudden upsets or shocks to the system. If you do it properly, then a lot of species will thrive better than ever in brackish waters.

Aaron Boyd
Aaron Boyd

Hello, I’m Aaron Boyd, the proud owner and author behind Aqua Movement. I hope my article was able to answer your questions. If you want to learn more about me, click the home icon above.

Aqua Movement