How to make saltwater for aquarium fish at home?

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This comprehensive guide details the process of creating saltwater for your aquatic pets, ensuring a safe and thriving environment. From essential equipment like thermometers and pumps to selecting the right sea salt mix, each element is meticulously outlined to streamline your DIY saltwater-making endeavor, whether you’re a novice aquarist venturing into the marine realm or a seasoned enthusiast seeking to refine your skills.

instant ocean sea salt
Instant ocean sea salt – Image by C-Reefer

Thus, many of us need to learn how to make saltwater for our aquarium fish at home.

Although it may seem simple, creating your own saltwater requires more than just mixing some salt and water together. Also, there’s no hard rule for the right amount of salt per each gallon of aquarium water, because that would depend on the salt mix you’re using.

I’ve made this step-by-step guide to help you along the way, so you can make your fish tank water safe for your pets with ease.

How to make saltwater for your aquarium fish at home?

How to make saltwater for aquarium?
How to make saltwater for aquarium?

In order to make saltwater, you will need a few pieces of equipment first. Here’s what you’ll need:

  • Submersible thermometer
  • Sea salt mix
  • Submersible pump or powerhead for water circulation
  • Hydrometer or refractometer to measure salinity
  • Water container
  • Aquarium heater

The first ingredient you’ll need to make seawater at home is marine salt.

There are several brands of sea salts available on the market, but from all of the ones I’ve tried, Instant Ocean is the most cost-efficient one. It’s relatively cheap, mixes clear, and gives you the same results as some of the more expensive brands.

Red sea salt is also a viable alternative, especially for reef tanks. It has a perfect blend of minerals that enhance coral growth and coloration.

As a side note, I would like to add that most fish stores also offer pre-mixed saltwater, but I wouldn’t recommend using it.

Its quality is questionable at best and you don’t know how long it has been sitting on the store shelf, collecting dust. I’ve also heard reports from fellow aquarists who have experienced algal blooms after using pre-mixed saltwater bought from their local fish store.

In terms of container size, you can use a simple plastic bucket to blend the seawater if your fish tank is going to be small. However, if that’s not the case, using a plastic drum would be a better idea.

That way, you’ll be able to prepare your saltwater in a single batch rather than mixing multiple ones.

Make sure the container you’re going to use is clean.

If it was used for other purposes and you suspect there might be trace amounts of contaminants left, you should buy a new one instead of trying to clean it.

In my experience with this, it’s better to be safe than sorry.

The few bucks you’ll save from buying a plastic bucket might end up costing you a fortune by destroying your entire tank.

Anyway, after making sure you have all of the necessary equipment at your disposal, you can move on to the actual process.

Here’s how to make saltwater for your fish tank at home:

1. Fill a container with dechlorinated water

fill container with water
Filling containers with water – Image by ajjw0828

You should avoid using plain tap water for your saltwater tank. That’s because it can severely harm or even be the end of your pet fish if it hasn’t been properly conditioned beforehand.

Water treatment facilities disinfect tap water with chlorine and chloramine which are toxic to fish. Apart from their toxicity, these substances also destroy the beneficial bacteria responsible for clearing up the waste in our aquariums.

Ideally, you’d have some distilled water at hand to use for your mix, but that’s rarely the case in any household. So to make tap water safe for your saltwater aquarium you should first dechlorinate it so you can get rid of the chlorine and chloramine.

This can either be done naturally or with a water conditioner. You can simply wait long enough for the Chlorine to gas out, but most tap water contains the more stable Chloramine.

Boiling is another method for natural dechlorination but it is basically impractical for fish-keeping purposes so just use some sort of aquarium water conditioner. Something like Seachem Prime should do the trick.

Author’s note: Since marine life is very sensitive to contaminants in water by definition most aquarists avoid using tap water for their tanks without purifying it. People usually use what’s known as a RO / DI system for the purification. An RO / DI system is a set of filters that run water from your tap through different purification processes such as Reverse Osmosis (RO) and Deionization (DI).

That being said there are people with successful fish tanks who do not use a RO / DI system for their tap water.

Anyway, when you’re measuring the amount of salt water for your fish tank, you should take into consideration that there should be some free space at the top to account for splashing and turbulence.

2. Place a water pump and a heater at the bottom of the container

mixing tank
Mixing tank – Image by DaddyFish

The rate at which the salt is going to dissolve will depend on the temperature of the water.

Salt dissolves slower in cold temperatures, so using a heater will decrease the time it takes to blend the saltwater.

The ideal temperature for this purpose would be between 75 and 78 °F (between 23.8 and 25.5 °C). Higher temperatures will only increase the risk of precipitation forming.

In addition to temperature, circulation also affects how fast salts get dissolved.

When salt particles are in motion, they get suspended in water which in turn forces them to dissolve at an increased rate.

By combining both methods, you’ll dramatically speed up the entire process and ensure there won’t be any salt residue afterward.

3. Add a sea salt mix into the water and stir

adding the sea salt
Adding the sea salt – Image by gatohoser

Before you add the salt mix into the water, carefully read the instructions on the box.

Although most brands recommend adding half a cup of sea salt per gallon of water, there are some exceptions to this rule.

It’s also a good idea to scoop up slightly less salt than what’s recommended on the label.

If the salinity is under the desired range, you can simply adjust it by adding more salt.

After you’ve read the instructions, proceed by gradually adding the sea salt to the water while stirring at the same time.

If you put the entire amount of salt into the container at once, it will settle at the bottom and form a residue.

Important: You should never add sea salt directly to an aquarium. Always mix saltwater separately and carefully monitor its salinity levels. Pouring marine salt directly into a tank that has living fish, invertebrates, or marine plants in it may cause them serious damage.

4. Use a refractometer or a hydrometer to measure the specific gravity of the water

hydrometer and salinity tester
Hydrometer and salinity tester – Image by Taxus812

After thoroughly mixing the salt solution, you should measure if it’s within the desired salinity range.

You can do this in one of two ways.

The first one is to use a hydrometer and test the “specific gravity” of the water.

To clarify: Specific gravity is a measurement of the density of a given substance to the density of a reference material. Substances with a specific gravity higher than 1 have a higher density than their reference material.

In our case, we’re using water as a reference material and comparing its density to that of salt.

Seawater typically has a specific gravity of about 1.025 to 1.026, so ideally, yours should mimic that.

The second and more reliable way to check if your water falls within the right salinity range is to use a refractometer.

Refractometers measure light refraction to determine the levels of salinity.

When light enters water it bends or refracts at a certain angle. The degree of this angle depends on the concentration of salt or other particles in the water.

By measuring this angle, refractometers also help us learn what the density of our solution is.

seawater refractometer
Seawater refractometer – Image by bpaston

Most saltwater refractometers usually have a scale in both PPT (parts per thousand) and Specific gravity.

In case you’re measuring the amount of salt in your saltwater solution in PPTs, you should aim for 35 PPT.

If after you mix the salt water, its salinity turns out under 35 PPT you should adjust by adding more sea salt.

To calculate the exact amount, you would need to add roughly 0.01 (4.44 grams) pounds of sea salt per a gallon (3.78 liters) of water for each PPT under the target value.

Let’s say your refractometer returns a reading of 33 PPT.

This means you would need to add 0.02 pounds of sea salt to the solution for every gallon of water to increase the salinity to 35 PPT.

This would equate to 2.4 pounds of sea salt for 120 gallons of water.

However, if the salinity is 34 PPT you would need to add half that amount or 1.2 pounds for the same volume of water. You can use this salinity calculator if you want to experiment with values.

This calculator is also quite useful if you’re trying to bring your water to brackish salinity. Anyway, when you’ve finished with the measurements, let the saltwater rest for 24 hours.

This should be enough for the levels of oxygen and carbon dioxide to reach a state of equilibrium. After the water has settled, return back to check its salinity again.

If it’s not within the specified range, adjust accordingly until you reach the desired level of salinity.

Don’t worry, it rarely happens that you’d need to adjust after the 24-hour mark.

My Final Words

marine fish aquarium
Marine fish aquarium – Image by William

Setting up a marine aquarium is a process that requires a certain set of skills.

By learning how to make saltwater for your aquarium fish, you gain a valuable skill that will aid you along your aquarium journey.

So what fish have you picked for your new tank? Here’s a list of fish ideas for complete beginners in this part of the hobby, if you haven’t chosen anything yet.

Share your plans for your new tank with other readers in the comment section.

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Momchil Boyanov is the Founder and now Senior Editor of AquAnswers. He has over 13+ years of experience in keeping home aquariums as well as providing professional aquarium services. Momchil has had his fair share of adventures in aquarium care. He has made MANY mistakes throughout his fishkeeping journey and thus learned A LOT. Through Aquanswers, Momchil shares knowledge about freshwater and saltwater aquariums with the people within this community.

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