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. Many aquarists get a little nervous about making brackish water, but in our opinion, it is quite easy for anyone who has kept freshwater tanks before. 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?

Let’s take a look at the pros and cons of this new venture before we jump into it. Brackish has the advantage of being able to

keep new kinds of aquatic species

, including:

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

Periophthalmus barbarous, Atlantic or West African Mudskipper

You can try breeding amano shrimp and nerite snails, whose offspring only survive in brackish 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. 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 are not dependent on a specific 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. 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

Brackish tanks can limit the number of plants and animals you can keep. Moreover, these species are sometimes hard to find since most fish stores don’t specialize in brackish water. You will need to take extra steps to maintain your tank. These include adding the correct amount of salt, and measuring the specific gravity of the water. Salt creep, or salt residue, can form in areas where water is sprayed out of tanks. You can wipe it off with a damp cloth, or place craft mesh on the tank lid holes to reduce 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. 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. They are slightly more costly than a hydrometer but they are easier to use and more accurate.

Refractometer is used to determine the specific gravity and amount of salt in water

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. Mangrove trees are the only plant that can withstand saltwater, even full fresh. To make our own tanks, we purchase mangrove seedlings via online sites. We then attach them to our aquariums with heavy duty wire. Once it starts growing more leaves, we have a dedicated light source shining on the mangrove to make sure it gets enough light. In brackish aquariums, you may need to occasionally wipe off any salt spray on the leaves to make sure it can still photosynthesize. 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.

We have also had success with java fern. However, it had to be slowly acclimated from freshwater to low end brackish water (SG of 1.005) over the course of two to three months. The plant is not dead, but it doesn’t grow fast. Anubias, hornwort and other “brackish” plants are not able to withstand low levels of salinity that is unacceptable for brackish animals. 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. For crushed coral and aragonite, you should rinse the substrate many times to avoid any cloudy water. 3. Place the aquarium on the stand, then add the substrate, decorations, and equipment. 4. You can fill the aquarium with dechlorinated waters. 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. For brackish water, fill the tank to 80% with fresh water. Then add 2 tablespoons (Tbsps) of reef salt per gallon. After approximately 8 hours, let the salt dissolve in the powerhead circulation or filter. Then 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. There are no differences in how to cycle a freshwater or brackish tank. But plants can be used more easily in brackish. Read our article on aquarium recycling.

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. The animals are kept in a quarantine area where salt is added to their bodies. This may result in some parasites or diseases being eliminated.

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. 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

Start concentration of 2 Tbsp Salt per Gallon

That means that you will need to add in 10 gallons worth of dechlorinated liquid and 20 tablespoons (20 or 1 1/4 cups) salt. Manufacturers of reef salt recommend premixing the water with salt in a container or bucket. Therefore, you can fill up two 5-gallon buckets with 10 Tbsp of salt each. 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. To speed up distribution, we prefer to pour it around the filter output and power head. 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.