how to make saltwater

How to make saltwater from reef salt mix

How do you make the saltwater for a saltwater reef tank?

Have you ever looked at a saltwater tank at a city aquarium, or even a dentist’s office and thought, “I wish I could have one of those!” but don’t even know where to begin? For example, where do they even get the saltwater for that reef tank from? Do you want to know how to make saltwater?

It’s no mystery, the saltwater from that reef tank came from one of three places:

If the location is near the ocean, it is possible, although unlikely, that they actually get their saltwater from the ocean. The ocean is a great place to get natural seawater for a saltwater reef aquarium, but it does have a few drawbacks:

  1. The water near civilization is sometimes less than pristine and may not be suitable for a home reef tank.
  2. Natural seawater may contain unwanted parasites or hitchhikers
  3. Harvesting seawater from the ocean can be labor intensive and logistically challenging

Three ways to make saltwater

Natural seawater from the ocean

Many reef aquarium hobbyists who want to eliminate the potential unknown factors associated with harvesting natural seawater, or for the vast majority of us who don’t live near the ocean, some will actually purchase their saltwater from their local fish store.

Saltwater purchased from a local fish store

Local fish stores typically have some sophisticated equipment, called a RODI filter, which purifies the water before converting it to saltwater for the reef tank. RODI stands for Reverse Osmosis De-Ionization, which describes the multi-step process this equipment performs to purify the water. RODI essentially filters tap water to make it pure water before the salt is added. The advantages of buying saltwater from a local fish store are that you don’t need to:

  • Purchase expensive equipment like a RODI filter to make the water
  • Perform any maintenance on the equipment
  • Spend any time to mix the saltwater yourself

However, buying saltwater at your local fish store can be expensive and still significant logistical challenges–especially for the aquarium hobbyist with a rather large saltwater reef tank.

Making saltwater from a reef salt mix

I believe the most common source for the saltwater used in a saltwater reef tank is to make saltwater from a reef salt mix. Simply purchase a high-quality salt mix and make the saltwater yourself. Don’t be alarmed, making saltwater from the salt mix can be as simple as making iced tea from a powdered beverage mix.

How to make saltwater from a reef salt mix

The process for how to make salt water for a reef tank is fairly simple and can really be done with just a few simple steps.

Step 1:

The first step is to purchase a high-quality reef salt mix. Your local fish store will likely have a selection of salt brands to choose from. If you aren’t sure which brand is right for you, I encourage you to check out my reef salt mix product review. These days, I get my salt online. It’s cheaper and I no longer have to worry about these heavy buckets rolling around in my trunk.

how to make saltwater step 1

Step 2:

When in doubt, read and follow the instructions on the reef salt mix package. Most salt mixes call for about 1/2 cup of reef salt for every gallon of freshwater–so use a measuring cup to measure out the salt precisely. Wear plastic gloves to protect your hands. The manufacturers tend to make recommendations on the light side. For example, the salt mix I personally use is Instant Ocean, which calls for 1/2 cup of salt mix for every gallon of water.

But this recipe makes water at a specific gravity of 1.021, which is fine for a fish only tank but is a bit low for a reef tank. To have reef-quality water, you will need to mix in more salt~ approximately 1/2 cup + 1-2 tablespoons per gallon.

how to make saltwater step 2

Scoop 1/2 cup (unless the package tells you differently) into a reef-safe, chemical-free bucket used only for mixing saltwater or performing water changes.

Step 3:

Depending on how much salt you measured into the bucket, you now want to add the correspondingly appropriate amount of water to that bucket. For example, if you added 4 x 1/2 cups (2 cups total) of salt mix, you want to add 4 gallons of water to the bucket and stir well, while the bucket fills up with water.

how to make saltwater Step 3

Step 4:

Use a small air pump and airline to aerate the water. Mixing the salt into the freshwater causes a chemical reaction and it takes some time for the chemical properties, like pH to stabilize. Aerating the water for a short time helps adjust the oxygen/carbon dioxide and pH levels.

how to make saltwater from a reef salt mix: Step 4


Step 5:

The last step in how to make saltwater you take before adding the saltwater to your tank is to use a hydrometer to measure the specific gravity of the water in order to confirm the water has the right amount of salt in it.

how to make saltwater step 5

use a hydrometer to measure the specific gravity

Generally speaking, when deciding how to make saltwater, you want a specific gravity of about  1.025, which is the specific gravity of natural seawater. As I mentioned earlier, you might need an additional 1-2 tablespoons of salt mix for every gallon of water, depending on the salt mix you use and the desired salinity. It is probably best to measure this all out, precisely, the first several times you do this and then as you get more comfortable you can probably get ‘pretty close’ just by creating a heaping scoop of the salt mix. But always test your water before and after adding to your aquarium to ensure your water parameters are in the right range.

Use a reef journal to track your readings over time to stay disciplined and look for any problems.

This process of how to make saltwater from a reef salt mix can get a bit more complicated if you don’t have a high quality, pure water coming from your tap. If there is a lot of chlorine in your municipal water, you may need to use a dechlorinator to purify your tap water first, or you may need your own RODI system to purify your water prior to use. But if you are a beginner in the saltwater aquarium world, I encourage you to start off small, with a nano aquarium, try out a fish-only aquarium first with a tried and true species, like captive-bred clownfish, and get some experience mixing the saltwater with tap water salt mix first–before you go crazy with all the extra purification equipment. Don’t get me wrong–the highest quality water will give you the best results, but depending on the size of your set-up and the purity required by the animals you plan to keep in your tank–all of that complexity and expense may not be warranted, so why not start out slowly–test, observe and see.

I hope that helps demystify the process of how to make saltwater from a reef salt mix. If you liked this article and want to take things to the next level, I encourage you to check out: The New Saltwater Aquarium Guide to learn more about what it takes to be a successful saltwater aquarium hobbyist.

A great place to learn more about how to make saltwater is the Instant Ocean product site. Instant Ocean is one of the most popular reef salt mix brands on the market.

Written by Albert B. Ulrich III–author of The Reef Aquarium Series of books:  The New Saltwater Aquarium Guide, How to Frag Corals, 107 Tips for the Marine Reef Aquarium.


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