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How to Make Saltwater | In 5 Easy Steps

If you’re just starting your first saltwater aquarium, you might be wondering how to make saltwater. After all, you can’t just dump some table salt in water: unfortunately, there are a few more steps involved.

Keep reading for everything you need to know about how to make saltwater at home!

How to make saltwater | What you’ll need

  • Mixing container (food grade)
  • Reef salt mix
  • Powerhead
  • Aquarium heater
  • Refractometer or hydrometer
  • RO-DI water
  • Measuring cups
  • Thermometer

Note: Does this all seem a bit daunting? We’d like to mention that you don’t necessarily have to make your own saltwater. Some aquarium shops also supply it. This does mean lots of lugging buckets around, and of course, you can unfortunately never be entirely sure of the quality of the water.

Aquarium stores might also supply RO-DI water, so you don’t have to buy your own RO-DI unit.

1. Fill your container with RO-DI water

Normal tap water in most areas is not the best option for making saltwater for your aquarium. It can contain high levels of nitrates or the mineral balance might be less than ideal.

The solution is RO-DI (reverse osmosis de-ionized) water. The simple explanation is that this is water that’s stripped of anything else that might have been in there, both the bad and good stuff. No worries: we’ll add the good back in later.

Don’t forget to always use a food-safe container that’s exclusively used for aquarium business and doesn’t contain residue from anything else. If you have a big tank and need lots of water, something on wheels can come in pretty handy.

2. Start up the powerhead and heater

The heater should be set to the temperature of your aquarium water. This ensures you don’t shock your fish when you add the new saltwater to your tank. It also helps the mixing process, as salt dissolves more quickly in warmer water.

The powerhead (or multiple, if you have some to spare) is there to help mix the salt once you add it in. It would be a bit too much work to sit there stirring the whole thing manually! You can also opt for an air stone.

3. Add the appropriate amount of salt

As mentioned in the intro, it’s crucial to understand that you can’t just use normal salt to mix saltwater for your marine aquarium. You need reef salt from an aquarium store. This is because it’s not just salt that you’re looking for, it’s also a range of minerals and other trace elements that comprise ocean water. Table salt just doesn’t contain these!

Reef salt is what you use to add all the good stuff back into your RO-DI water while keeping the bad out. This allows you to create a perfectly balanced mix, just how your fish and corals like it.

Be sure to read the instructions that come with your specific salt mix, as different ones have different properties. Use a measuring cup to measure out the right amount. It’ll usually be ½ cup per gallon plus possibly a little extra to reach a specific gravity of around 1.025.

Saltwater reef aquarium | How to make saltwater

4. Wait

Once you’ve turned on the equipment and added the salt, it’s time to sit back and let the powerhead do its work of mixing and aerating.

Don’t get impatient: it can take a bit for the pH of the water to settle once all the chemicals are dissolved. The instructions on your salt mix may state how long the mixture needs.

5. Test salinity

Once all the salt has dissolved and the initial cloudiness of the water has disappeared, your fresh saltwater should hopefully be ready to use. Still, you should always test it to make sure. A refractometer is considered the most accurate equipment for measuring salt levels, but you can also use a floating hydrometer.

What you’re looking for is a specific gravity of 1.023-1.026, with 1.025 being perfect for most tanks. That’s around 35 parts per mille.

Don’t forget to also double-check the temperature before using this new water for a water change. It should be the same as the temperature in your aquarium.


Does the idea of mixing your own saltwater for the aquarium seem like a bit too much of a daunting task? No worries! FantaSEA Aquariums doesn’t just design and build custom aquariums, we also maintain them. Contact us here if you need help with your tank! You can also feel free to contact us if you still have more questions about how to make saltwater.

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Marijke Puts

Hey! I'm Marijke, FantaSEA's resident blog writer. I'm a full-time pop science author, part-time PADI diver and snorkeler, and have been keeping fish since I was a kid. When I'm not writing fish care guides, you can usually find me underwater or trying to figure out how to fit more tanks into my house.

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