How To Set Up A Brackish Water Aquarium (Complete Guide)

If you are looking for something new to experience in the aquarium hobby, you might want to give brackish tanks a try.

brackish aquarium set up guide


Brackish water aquariums are very unique as they are not a saltwater tank nor a freshwater tank. They are kind of in-between. They are a mix of both containing similar characteristics.

Before you consider setting up a new brackish water tank, it’s important to do proper research and use the information to help you set up a successful brackish water tank.

This article is an overview of how to set up and maintain a brackish water aquarium properly.


What is brackish water?


Brackish water is water that has more salinity than freshwater but not as much as seawater. Think of it as freshwater that has salt in it but not as much as we would keep our saltwater tanks at. The salinity levels are much lower in brackish than they are in seawater. 


Setting up a brackish water tank


Natural habitat and environment



Brackish water occurs when freshwater rivers meet with seawater creating habitats that are a mix of saltwater and freshwater. 

These are naturally found in coastal streams, estuary, and sea swamps.  Due to the changes in the environment, the salinity level of these areas can change quite often and the water parameters are not always consistent or the same. Fish and other organisms move to areas as these conditions change.


Coastal streams 


These brackish environments are found near the coastline and have a salinity level of around 1.0002 or 7-14ppt. Mostly livebearers can be found there like guppies and mollies. 




This is a body of water that is very slow-moving. If you plan to create an estuary environment in your aquarium, ensure that there is very little water movement and use plenty of rocks, branches, and other decorations. The salinity level in these areas ranges from 1.020-1.025.  

Sea swamps 



This is probably the most common brackish water environment that people create in their home aquarium. Sea swamps are found in many places throughout the world where you will see mangroves and tree roots that grow in the water but the branches and leaves are just above the water surface. These muddy and swampy areas generally have salinity levels of 1.005 and 1.010.


Water requirements


As mentioned above, brackish water is a mix of freshwater and saltwater. The salinity of the ocean and our saltwater tanks is around 35ppt or 1.025 specific gravity.

The specific gravity of freshwater is 1.000. Brackish water will range between 1.005 and 1.012 SG. Brackish water will also have a higher PH and alkalinity than freshwater.

So when you are setting up your brackish tank, you will want your salinity to measure 1.005-1.012 SG.


Brackish water parameters:

PH: 7.8-8.4

ALK: 10-18 kh

Temp: 72-82F

Nitrate: <50 ppm

Nitrite: 0

Ammonia: 0

General Hardness: 12-20 GH


Tank size


You can use any sized tank that you like when setting up a brackish tank. There is no minimum or maximum size. But the same rules apply when choosing the appropriately sized fish for the tank. If you choose a smaller size aquarium, you will be limited to smaller fish.

A larger tank above 30 gallons will give you more options. Many brackish fish are active and need plenty of swimming space. 




As with all aquariums, filtration is important. You will need to maintain excellent filtration on your brackish aquarium. You can use a hang on back filter, canister filter, internal filter, or a sump system. 


Substrate for brackish tanks


When choosing the type of substrate for your brackish tank, you will want to replicate the natural environments. You can use a sand or gravel base or a mix of both. Crushed coral and aragonite sand is also popular as this will help maintain PH and hardness water levels. 




Specific lighting for a brackish water tank is not a requirement like it is for a saltwater reef tank or freshwater planted tank. If you are keeping a fish only tank, then a basic LED, T5, or T8 lighting will be sufficient. Any light that is aquarium safe and makes the tank and fish look good will work fine.

If you are keeping plants in your tank, you will need to make sure your light is suitable for maintaining plant life.


Cycling a new brackish water tank


Before adding fish to your new tank, it’s necessary that the tank has completed it’s cycle. It can take many weeks for an aquarium to finish cycling and become safe for adding fish.

This is where beneficial bacteria will form naturally throughout your tank. Over a period of 4-8 weeks, the bacteria will begin to breakdown harmful ammonia into nitrite and then into nitrate. This process happens with all aquariums and you will need to be patient as it does take time.

Rushing a new tank is never a good idea and things work out much better if you take your time and let things happen naturally over time. Once your nitrate level reads 0, your tank is cycled.


Adding new fish



Once your tank has finished it’s cycling and you tested all your water parameters to make sure they are within limits, you can gradually begin to add fish.

If you add too many fish early or all at the same time, this can really mess up your new cycle and cause problems. I recommend that you only add 1 fish at a time depending on your tank and fish size. If you are keeping smaller brackish fish, you can add a few at a time.

After adding the first fish, wait a few days, and test your water. If everything is good, you can add another fish. Always acclimate new fish to ensure a smooth transition into your tank. 




Regular maintenance with a brackish water tank includes regular water changes, tank cleaning, equipment cleaning and testing, water tests, etc. All the normal maintenance items that you would perform on a freshwater or saltwater tank apply to a brackish tank.

The biggest factor in maintaining a brackish water tank is keeping the proper salinity level. If the salinity level gets too high or too low, it can affect the health of fish, plants, and other livestock like crabs. Use a quality hydrometer or refractometer to measure the salinity level on a regular basis.

An important factor to consider is water will naturally evaporate from your tank leaving the salt behind. So the salinity of the water will increase naturally and you will need to replenish the tank with freshwater. 


How much salt do you need to make brackish water?


Now that we know that brackish water measures in the range from 1.005 and 1.012 SG, let’s discuss how to achieve those numbers. Depending on the salt manufacturer, you should aim to add ⅛ cup of salt per gallon of freshwater.

This can vary so make sure you test often with a hydrometer or refractometer. If you add too much salt and end up with a higher number, add fresh water to bring it down. If you don’t add enough salt, the salinity will measure too low and you can add more salt to bring it up within range. 

For example, if you are setting up a new 40-gallon brackish water tank, you will want to pre-mix the water before adding it into your tank.

You should use a heater to bring the temperature within range and a powerhead to mix the salt with the water.

Adding ⅛ cup for each gallon of water means that you will need about 5 cups of salt for that sized tank. I recommend you have more salt on hand just in case you underestimate. 


What types of salt do you need for brackish water tanks?


When choosing the type of salt for your brackish water tank, you should use a marine salt mix instead of freshwater aquarium salt. The same salt that you use in a saltwater aquarium should be used in a brackish water tank. Instant Ocean or Red Sea are both excellent brands that you can use.

Keep in mind that not all salts mix the same. Some will mix faster than others and have a recommended mixing time at a certain temperature.

Brackish fish types



There are many different brackish water fish available to keep in your aquarium. Here are some common types:

  • Knight Goby                    
  • Figure 8 Puffer                          
  • Green / Red / Silver Scat
  • Skunk Goby
  • Spotted Puffer
  • Bumble Bee Goby
  • Colombian Shark Catfish
  • Mono Sebae
  • Golden Puffer
  • Mono Argentus
  • Archer Fish
  • Datnoid
  • Green or Orange Chromide



Can freshwater fish adapt to brackish water?


There are a few fish that can adapt to brackish water. The most common ones being Fancy Guppies and Sailfin Mollies. These are both readily available in stores and commonly seen in home aquariums.




While many hobbyists are more familiar with saltwater and freshwater tanks, brackish water tanks are still popular. They are very unique and you can do some great things with aquascaping and mixing varieties of fish. Many aspects of fishkeeping are similar, the biggest difference with brackish water tanks is the salinity level. If you have always wondered about keeping a brackish water tank, I suggest you give it a try. They are impressive and always make an excellent conversation piece.