How To Mix Saltwater for an Aquarium (A step by step guide)

Photo of author

by Jason Matthews



Keeping a saltwater aquarium opens up a new world of fish species and plant life to admire and enjoy. Coral, Dragon’s Tongue algae, clownfish, and mollies are some of the spectacular and beautiful plants and fish you can only enjoy in a saltwater aquarium.

If you’re setting up your first saltwater aquarium or have only kept freshwater fish, you may be wondering if you can make your own salt water. The answer is, yes, you can! However, it is not as easy as adding table salt to tap water.

Buy a premade dry synthetic saltwater mix from an aquarium store. Follow the directions to add it to freshwater, then closely monitor the water conditions to ensure you have the proper balance of minerals. Mixing saltwater for your home aquarium is not complicated, but you must do it correctly to ensure the health of your fish and plant life. Read on to learn how to mix saltwater for an aquarium.

Can You Use Seawater in a Saltwater Aquarium?

If you live by the ocean, you may be tempted to walk down to the beach and simply scoop up a bucket full of seawater for your tank. Unfortunately, this is not a good idea.

Natural seawater contains a lot of variables that are difficult to control. For one thing, the water at most of our beaches is less clean than we’d like to think. Contaminants like oil, microplastics, and residue from street runoff are all present to some degree in most of the water near our shores.

Secondly, seawater often contains parasites and other hitchhikers. While fish in the sea may have adapted or become resilient against these parasites, fish raised in tanks are unprepared to handle them.

Finally, scooping up seawater is labor-intensive and difficult. You need to change the water in your tank regularly to ensure that the ecosystem remains balanced and the fish stay healthy. Are you sure you want to slog down to the beach every time you need to change your aquarium’s water?

Good Sources of Aquarium Tank Saltwater

Now that we’ve established that using natural seawater is not a good idea for a home saltwater aquarium, let’s look at some ways you can source saltwater for your tank.

Buy Premixed Saltwater From Your Aquarium Store

Most aquarium shops sell pre-made saltwater. One of your local stores likely has a RODI (Reverse Osmosis Deionization) filter for purifying fresh water. Once the water has been purified, the shop adds the right amount of high-quality salt to create water with the correct mineral balance for saltwater life.

The advantage of buying premixed saltwater from a store is that you know the salt balance will be correct, and you don’t need to invest in any special RODI equipment to make it yourself.

Make Your Own Saltwater Using Reef Salt

The downside of buying pre-made saltwater from a marine store is that it is expensive. It’s also very heavy and can be difficult to transport.

It is not too hard to make saltwater for your aquarium at home. We’ve broken the process down into seven steps:

  1. Purchase a high-quality reef salt or sea salt mix

Last update on 2023-06-05 / Affiliate links / Images from Amazon Product Advertising API

These days, the easiest place to find good reef salt is online. It’s also much easier to get it delivered than to haul it back from the pet store. Look for “reef salt,” “reef crystals,” “sea salt” or “coral salt.” 

Make sure that if you plan to have coral in your tank you are not purchasing “aquarium salt” by mistake. Aquarium salt is not the same thing as reef salt. Aquarium salt does not have the calcium content to support coral.

  1. Purchase RO or Deionized Water

Either buy filtered water or filter your tap water. It is better to use filtered water in a saltwater aquarium because tap water contains unpredictable levels of minerals, metals, and other contaminants.

  1. Clean your tank and all materials

 Rinse your tank with fresh water and leave it to dry. Rinsing will remove any particulates or contaminants from the tank. Do the same with any other materials you plan to use while mixing the salt or filling the tank.

We recommend having a second tank or bucket as large or larger than the tank you intend to fill. Mix the saltwater solution in this before transferring it to the final tank.

  1. Measure ½ cup of salt for every gallon of water

Follow the directions on the label of the reef salt you purchased. In general, ½ cup of salt to one gallon of water is the correct mix. Pour all of the water into your mixing bucket and then slowly add the salt while continuously stirring.

  1. Aerate the water

Use a small pump and airline to aerate the water. Mixing salt into freshwater creates a chemical reaction, and it takes some time for the PH levels and other chemical properties to stabilize. Aerating helps to speed up this process.

  1. Let the solution sit for 24 hours

Once the salt water is mixed, let it stand for at least 24 hours. This gives the chemicals time to stabilize and also lets the water come to the right temperature. Measure your PH levels, temperature, and TDS levels to make sure that all parameters are where they should be.

  1. Measure the specific gravity

Last update on 2023-06-05 / Affiliate links / Images from Amazon Product Advertising API

As well as chemical levels and temperature, you should also measure the specific gravity of the saltwater. You will need a hydrometer to do this. The specific gravity of the mixture should be 1.025 if you want to emulate natural seawater.

Some of the instructions on leading reef salt brands can lead to a solution with a lower specific gravity (1.021 or so). If you prefer a higher specific gravity for your saltwater, stick with the ½ cup of salt per 1 gallon of water measure.

Related article: Read how to make tap water safe for saltwater aquariums

Monitor Your Saltwater Tank

After you add the saltwater to your tank, carefully monitor it for at least 48 hours before adding fish. Continue to check the temperature, specific gravity, and PH levels. Once you are satisfied that conditions are stable, you can add your desired plants and fish.


Jason Matthews

My name is Jason Matthews, and welcome to my website. When other kids were bragging about how their dog could sit and roll over, I was bragging about my latest Betta Fish and the cool sea castle I just added to his aquarium. 

Jason aquariume

🐠 Get Your Free Ebook: A Beginner's Guide to Aquariums - Sign Up Now!

Learn everything you need to know to keep fish, including setting up your tank, choosing the right fish, and maintaining water quality. As a subscriber, you'll also stay up-to-date on the latest aquarium products, special offers, and discounts.

Your privacy is important to us. You can trust that we will never share or sell your information, and we'll only send you relevant content.

Leave a Comment