How to Set Up (and Maintain) a Brackish Aquarium

If you have been keeping freshwater aquariums for a while, you may feel like you’ve already tried everything in the hobby, such as nano tanks, aquascaping, African cichlids, and ponds. Consider setting up your first brackish fish tank that will allow you to try an entirely new category of animals. Although many aquarists are nervous about creating brackish water from freshwater tanks, we believe it is possible. Learn what it takes to create and maintain your first brackish aquarium in this step-by-step guide.

Brackish Water Tanks: What are the Pros and Cons?

Before you jump in to this new venture, we need to weigh the benefits and decide if a brackish tank is right for us. The main benefit of going brackish is the ability to

Keep new species of aquatic animals

, including:

– Green spotted puffer (Dichotomyctere nigroviridis) – Figure 8 puffer (Dichotomyctere ocellatus or Tetraodon biocellatus) – Bumblebee goby (Brachygobius spp.) – Knight goby, Stigmatogobius sadanundio – Mudskipper, Periophthalmus species spp. – Banded archerfish (Toxotes jaculatrix) – Red claw crab (Perisesarma bidens)

Periophthalmus barbarous, Atlantic or West African Mudskipper

You could also try breeding nerite snails and amano shrimp, which can only survive in brackish waters. Plus, certain freshwater fish like guppies and mollies can do well in brackish water.

Brackish water is a great choice for certain species of livebearers because it contains all the necessary trace minerals and water parameters to maintain their optimal health. Plus, many freshwater diseases and parasites cannot survive in brackish water. Therefore, fish farms often breed livebearers in part fresh and part salt water to raise healthier stock and save costs.

Brackish aquariums don’t require any specific amount of salt. Brackish species, unlike corals in saltwater reef aquariums, can withstand fluctuating water conditions. They live in estuaries that are where rivers and streams meet with the ocean. Depending on the tides or rainfall, they can experience full fresh water or full salt water all within the same day. Your fish will be fine as long as they have the bare minimum amount of salt (see below for more details).

Estuary California, where fresh water is mixed with salt water

Conversely, brackish tanks do limit you on the types of animals and plants you can keep. Moreover, these species are sometimes hard to find since most fish stores don’t specialize in brackish water. There are additional steps that must be taken to maintain a tank, such as adding the proper amount of salt or measuring the specific gravity (SG). Finally, salt creep or leftover salt residue can occur in areas where water splashes out of the tank, but you can easily wipe it off with a damp cloth or install some craft mesh over the tank lid holes to mitigate it.

Materials List for a Brackish Aquarium

The supplies you need for a brackish tank are almost exactly the same as a freshwater tank – such as a fish tank, aquarium stand (optional), lid, light, heater, thermometer, filter, dechlorinator, and aquarium siphon. You can choose from regular gravel, sand or other inert materials for your substrate. However, if you have soft water with low pH, we highly recommend getting aragonite or crushed coral to help buffer the water and replicate a semi-marine environment.

The salt must be marine or reef salt and not regular aquarium salt. While aquarium salt is sodium chloride (NaCl), marine salt has sodium chloride as well as many essential minerals like magnesium, potassium and calcium. To measure the specific gravity of the water, a refractometer (SG) is recommended. Although they may be slightly more expensive than a Hydrometer, we believe they are more accurate and more user-friendly, especially as you don’t have your hands get wet.

Refractometer to measure the specific gravity of water or the amount of salt in it

Which plants can live in brackish waters? Although the internet is filled with lists of brackish-safe plant names, we have found that most plants will struggle to withstand salt water. The mangrove tree is the only surefire plant we know of that handles everything from full fresh to full salt water. We purchase live mangrove seedlings online and hang them on our tanks using heavy-duty wire. This ensures that no water is left at the ends of the leaves. Once it starts growing more leaves, we have a dedicated light source shining on the mangrove to make sure it gets enough light. To ensure that the mangrove can continue to photosynthesize in brackish aquariums you might need to periodically wipe off salt spray. Once the mangrove has reached a height of at least 10 feet, you can put it in an aquarium that has a deeper substrate. To feed it, add root tabs.

Java fern is another plant that we have had success. It had to be gradually acclimated over a period of two to three weeks from freshwater to low-end brackish water (SG 1.005). The plant is not dead, but it doesn’t grow fast. Other “brackish”, such as anubias or hornwort, can only handle very low salinity levels, which is not acceptable for most brackish species. For more information on hobbyists’ experiences with brackish water plants, see this forum post.

Java fern (Microsorum pteropus)

How to Set Up a Brackish Aquarium

The instructions for installing a freshwater aquarium are similar, so let’s focus on how to prepare it. You want to get to a

specific gravity between 1.004-1.012

. We personally keep most of our brackish tanks at 1.005-1.008.

1. Find a location for the fish tank and assemble the aquarium stand if needed. 2. Use fresh water to rinse the tank and accessories. If using aragonite or crushed coral, make sure to rinse the substrate multiple times to minimize cloudy water issues. 3. Add the decorations, equipment and substrate to the aquarium. 4. Dechlorinated water should be added to the aquarium. 1. If you plan on slowly acclimating your fish and plants from fresh water to brackish water, then just add normal drinking water as usual without any salt. 2. If you want brackish water from the start, fill 80% of the tank with fresh water and scoop in 2 tablespoons (Tbsp) of reef salt per gallon of water. Allow the salt to dissolve in the filter or powerhead circulation. After about 8 hours, check the specific gravity. Depending on what the refractometer reads, you can add fresh water or marine salt to the tank until the desired SG has been reached.

If this is a brand-new setup, you need to cycle your aquarium before adding any fish to ensure that the fish tank’s ecosystem can safely process the toxic ammonia produce by your fish’s waste. You can cycle a freshwater tank or a brackish one the same way. However, brackish water is more difficult for plants to use. Please see our article about aquarium cycling.

Knight goby (Stigmatogobius sadanundio)

How to Acclimate New Fish for a Brackish Tank

Most brackish fish that are sold at fish stores are usually kept in freshwater environments. If you are purchasing brackish fish, it is necessary to slowly adapt their bodies to the saltwater environment over a period of at least four weeks. To set up a freshwater aquarium, follow Step 4a. Once it is cycled, add the fish and slowly add marine salt over the course of four weeks until you achieve the required SG.

If you already have an established brackish aquarium with fish and you want to add new animals that are accustomed to fresh water, set up a separate quarantine tank or tub that is fully fresh water. Use the same procedure as before to raise the SG incrementally until it matches the tank. Because the animals are in a quarantine system where salt is being added, some parasites and diseases may be eliminated in the process, which is a nice side benefit.

Banded archerfish (Toxotes jaculatrix)

How to change water and maintain a brackish water tank

When it comes to tank maintenance, the steps are exactly the same except for the water preparation. You must track the amount of water removed from the tank to maintain the same salt content. For example, let’s say you decide to do a 50% water change on a 20-gallon aquarium.

Based on our

Starting concentration: 2 Tbsp salt per gallon

This means that you’ll need to add 10 gallons dechlorinated water, 20 tablespoons (or 1 1/4 cups) of salt. Manufacturers of reef salt recommend premixing the water with salt in a container or bucket. You can fill two 5-gallon buckets of 5 gallons with 10 tbsp each salt. You can mix large quantities of water with a powerhead or stir the salt by hand. Marine salt is very fast to dissolve. Pour the brackish water into the aquarium and then measure the tank’s SG after a few hours have passed. Salt can be added to the tank to increase its SG. You can also remove any tank water from the aquarium and replace it with dechlorinated fresh water to lower the SG.

Remember that brackish fish can live in a wide range of salinity, so do not worry too much about adding salt directly into the tank if needed. We like to dump it around the filter output or power head for faster distribution. Also, if the water in the aquarium is too low and you need to top off (or replace) the evaporated water, add fresh water only. Salt doesn’t evaporate so don’t add brackish water to your aquarium or the SG will rise.

How frequently should you test for salt? After every water change, we test the SG within a few hours to the next day.

Bumblebee goby (Brachygobius dorae).

Brackish water tanks are a great way to have fun, especially when you think about all the species you can keep. They are much easier than saltwater reef tanks, and if you are confident with keeping freshwater aquariums, you will be successful with brackish ones. If you have any more questions, please visit our forum and many experienced brackish fishkeepers will be happy to help you.