How to Set Up (and Maintain) a Brackish Aquarium

If you’ve been keeping freshwater aquariums for some time, it may seem like you’ve tried every aspect of the hobby such as aquascaping and African cichlids. 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. This step-by-step guide will show you how to make and maintain your first brackish tank.

Brackish Water Tanks: What are the Pros and Cons?

Before we dive into this new venture, let’s consider the pros and cons to see if it is worth your while. 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 can also breed nerite or amano shrimps. However, their offspring cannot survive in salt water. Plus, certain freshwater fish like guppies and mollies can do well in brackish water.

One of the advantages of putting certain livebearers in a brackish tank is that brackish water contains all the trace minerals and water parameters necessary for maintaining optimal health in these species. Brackish water also prevents many freshwater parasites from thriving. Therefore, fish farms often breed livebearers in part fresh and part salt water to raise healthier stock and save costs.

Also, put your mind at ease because brackish aquariums do not require a precise amount of salt. Brackish species can adapt to changing conditions unlike corals in saltwater aquariums. This is because they live near rivers and streams that meet the ocean. You can give your fish either full fresh water or complete salt water depending on how the tides or rain affect them. Your fish will be fine as long as they have the bare minimum amount of salt (see below for more details).

Estuary in California where fresh water mixes with salt water

Brackish tanks, however, do restrict the kinds of animals and plants that you can keep. Moreover, these species are sometimes hard to find since most fish stores don’t specialize in brackish water. Some additional steps are required to maintain tanks, including adding the right amount of salt and measuring its 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. For substrate, you have the option of using regular gravel, normal sand, or any other inert product. We recommend aragonite or crushed coral for soft water with low pH. This will help to buffer the water and recreate a semimarine environment.

You must purchase marine salt for saltwater aquariums and not the regular aquarium salt for freshwater. While aquarium salt is sodium chloride (NaCl), marine salt has sodium chloride as well as many essential minerals like magnesium, potassium and calcium. A refractometer is a device that measures specific gravity (SG) in water to determine the salt content. Yes, they are slightly more expensive than a hydrometer, but we find them to be more accurate and easier to use, especially since you don’t have to get your hands wet in the process.

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

What plants can survive in brackish water? We have seen many lists on the internet of plants that are safe for brackish water, but we found that most plants suffer when salt is added. The mangrove tree is the only surefire plant we know of that handles everything from full fresh to full salt water. To make our own tanks, we purchase mangrove seedlings via online sites. We then attach them to our tanks with heavy duty wire. It will start to grow more leaves so we put a dedicated light bulb on it. If you have brackish fish tanks, it may be necessary to wipe off salt spray from the leaves occasionally to allow them to photosynthesise. Once your mangrove grows tall enough, you can place it in an aquarium with a deeper substrate. You can also add root tabs for feeding.

We have also had success with java fern. The plant had to be slowly adjusted from freshwater into low end brackish (SG of 1.055) over the next two to three months. While the plant has not died, it does not grow very quickly either. Anubias and Hornwort are the only “brackish”, commonly available, plants that can handle low levels of sodium. This is not acceptable for most brackish animal species. See this forum post for more details on other hobbyists’ experience with brackish water plants.

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. It is our goal to make the water as clean and clear as possible.

Specific gravity ranges from 1.004 to 1.012

. Our brackish tanks are kept at 1.005 to 1.008.

1. Find a location for the fish tank and assemble the aquarium stand if needed. 2. Wash the accessories and tank in clean, running water. For crushed coral and aragonite, you should rinse the substrate many times to avoid any cloudiness. 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. You can get brackish water right from the beginning by filling 80% of your tank with fresh water. Next, add 2 tablespoons (2 Tbsp) reef salt per gallon. Allow the salt to dissolve in the filter or powerhead circulation. After about 8 hours, check the specific gravity. Depending upon the reading of the refractometer, add more water and salt until you reach the desired SG.

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. A freshwater tank can be cycled in the same manner as a brackish aquarium. However, plants are more difficult to use in brackish waters. For more information on aquarium cycling, please refer to our article 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. Step 4a is required to set up a new aquarium. 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. Continue to increase the SG slowly until it is equal to your existing tank. You may find that some parasites, diseases, and other problems are eliminated while the animals remain in quarantine.

Banded archerfish (Toxotes jaculatrix)

How to Change Water and Maintain a Brackish Water Tank

The steps for tank maintenance are identical, except that of the water preparation. Because salt is taken out during water changes, you must keep track of how much water is removed to keep the salinity the same. 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. The preferred method recommended by reef salt manufacturers is to premix the water and salt in a bucket or tub. Two 5-gallon containers can be filled with 10 Tbsp salt each. It is easy to dissolve marine salt. To mix large volumes of water, you can use a powerhead, an air stone or stir it by hand. 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 often should you check salinity? We test the SG after every water change, usually within a few hours or the next day.

Bumblebee-goby (Brachygobius doniae).

Brackish water tanks can make keeping fish very exciting, especially when you consider the many species you can get. 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.