Mix up the best saltwater! A step by step beginners guide to mixing reef aquarium water

Creating artificial seawater at home is pretty simple and all you need is the salt mix, RO/DI water, a mixing container and a small pump or powerhead.

Mixing Station

The most commonly used saltwater mixing and storage container is a Rubbermaid BRUTE trash can. They have been used by reefers for decades which means they are safe and readily available at most big box hardware stores.

You can never really have too much saltwater on hand but you need something large enough to hold at least 50% of your total display tank water volume. For a 40 gallon tank, you need a minimum of a 20-gallon container but something closer to 40 gallons would be best. Using a tight-fitting lid is also recommended to keep out debris and reduce evaporation effects.

Brute Trash Cans at Home Depot

It is best to use a float valve so your RO/DI system can fill the BRUTE container and automatically turn off when full. Having two containers is the easiest route, one for freshwater and one for saltwater. To attach a single RO water line, you will need a push to connect tee fitting and a couple of valves to route water into both containers. You can alternatively use a three-way valve to direct water between the two containers.

Salt Mix

The best way to look at salt mix is that all of the popular brands are going to be a decent option. You have dozens of options and just choose one that speaks to you, and go with it. You shouldn’t be changing salt mix brands abruptly so keep that in mind.

Salt Mix at BulkReefSupply.com

We selected Tropic Marine Pro Reef for our tanks here at BRS based experience and a few distinct criteria. Once mixed, it stores better than some of the others meaning it maintains stable parameters and does not produce residue or precipitate. It will maintain this quality through multiple weeks and even months of proper storage. We have also tested parameters from different buckets of Tropic Marine salt mix and get very consistent results between the different batches.

Pouring salt mix into Brute container

How To Mix Saltwater

Most salts have somewhat different mixing procedures; some require heating and/or maybe some circulation with a pump. Point is, simply read the instructions on the bucket and follow them accurately for the best results. Trust us when we say, it really does matter. For Tropic Marin Pro, these are the basic steps.

1. Turn on a flow pump or powerhead in the bottom of the BRUTE trash can with the desired amount of water. Remember, RO/DI WATER ONLY!

2. Start adding the salt at the rate of about 2 - 2.5 cups per 5 gallons of freshwater.

3. Measure salinity using a refractometer after a few minutes of letting it mix up. Target Salinity = 35 PPT

4. Adjust salinity as necessary using a little more freshwater if the mix is too salty or a little more salt if it is too diluted.

It is important that you add the salt to the full amount of water you want to make. If you add water to the dry salt or make a concentrated solution it causes crusty precipitation and creates an inconsistent mix.

Using the right amount of salt is important and the 2 - 2.5 cups per 5 gallons of water is only a guideline that is specific to Tropic Marin Pro Reef. Most reefers will mix the same amount of water every time and use the same measuring cup. After a few times of mixing, you can become accustomed to gauging the amount of salt to get within a reasonable range of your desired salinity. Check out our selection of OXO brand measuring devices and tools to help get the job done!


Natural seawater averages a salinity level of 35 parts per thousand (PPT).

A refractometer is your best choice for measuring the salinity; gently place a few droplets of saltwater onto the lens, close the lid, give it a few minutes for temperature to equalize then look through the eyepiece under sufficient lighting.

Refractometer Scale

The salinity level is indicated by the distinct line created by a change in color. We use part per thousand or PPT which is the most accurate measurement for seawater. There are also digital refractometers that give you a digital readout with a push of a button.

The amount of time your salt mix takes to fully dissolve can vary among the brands, just follow the instructions in terms of mixing time. The Tropic Marin Pro mixes up fast, within just a few hours, which is just another reason we prefer it here at BRS.

An aquarium heater is not really required for water exchanges less than 25% of your total system volume. If you are doing larger water changes, then you may want to consider heating the mixed saltwater before adding it to your tank. This will avoid drastic temperature swings that will surely stress out your fish and corals. At less than 25%, temperature effects will be minimal if not null.

Brute Trash Can

How To Store Mixed Saltwater

Yes, you can safely store your mixed saltwater for use at a later date. Many hobbyists mix salt in large batches for use over the course of 2-6 weeks and sometimes longer. Not all salt mix is created equal and storage is affected in this case.

Tropic Marin salt stores very well as long as you utilize a tight-fitting lid which will reduce evaporation. It will not leave any residue, brown crust or contaminates because of the strict quality control and pharmaceutical grade chemicals. Once mixed, the chemistry remains stable so you can easily get 2-3 months of storage with Tropic Marin Pro. With the right size storage bin and water change schedule, that means you can get away with only mixing salt a few times per year.

Filling Your Reef Tank With Saltwater

Now that we have mixed saltwater, it is time to fill the tank. If you want to prevent sand from blowing around and creating a cloud, you can pour the water into a smaller container inside the tank and let it overflow. Using the clarifier included with Caribsea live sand helps clear up the cloud.

After filling the tank, turn on your powerheads or flow pumps to help clear up the cloud inside your display. This brings us to our next topic in the series which is all about water flow inside saltwater reef aquariums.

5 Minute Saltwater Aquarium Guide Episode 11

Looking for a different topic or have questions? You can binge the entire 5 Minute Saltwater Aquarium Guide playlist right here on our website. We also invite you to join the #askBRStv Facebook Group which is a free resource for you to ask questions, get advice, interact with other hobbyists and get your daily reef aquarium fix.

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