Ideal Saltiness of your Aquarium

By Nadine Oraby | 2020 Update


On average, the air around us contains 20.95% oxygen.

Imagine if that figure went up to 50% OR reduced to 5%.

We would most probably suffer while breathing and then eventually depart from this beautiful planet.

Likewise, the sea has a certain amount of salt in it to keep the fish alive.

Lesson Learnt:

An aquarium should also include some salt to give your pet fishes a livable environment.

So let’s get to the point, what is the ideal saltiness of your aquarium? Well, as per general rules, 35 PPT is the average accepted level of saltiness that shall be maintained in your aquarium. 35 PPT, i.e. parts per thousand means the after every 35 parts of salt is 1000 parts of water OR in mathematical terms 3.5% of water.

Now let’s talk about different aspects of ideal saltiness of your aquarium step by step.

What is the Saltiness of Water?

Water, as per its properties by default has some salt in it whether it is seawater or freshwater; however, the quantity dramatically varies.

When mixed with water, salt dissolves that is why it cannot be physically seen.

However, if we boil water and evaporate it completely, the residue left behind is salt.

Of course, practically this is not how you will measure the salt of your aquarium, or else it would take up most of our lives.

Well maybe in the ancient times, this is how it would have been measured, but in modern times various devices are used saltiness of your aquarium:

Hydrometer, refractometer, and an electronic salinity meter.

Seawater Composition

Freshwater vs. Saltwater

The amount of salt you should add depends on the type of water that you are using.

Well, of course, seawater is not available most of the time as not everyone lives close to the beaches.

Freshwater and artificial seawater is also purchased by the pet owners.

As freshwater is widely used for the aquarium with salt being mixed, it will be the focus of this article.

Fish Vet’s advice on using salt for freshwater fish in aquariums (Video)

Ideal Saltinity for your Aquarium

The level of saltiness of your aquarium would depend on the fish and plants you have.

The overall aim is to provide a natural environment for your fishes.

Following are the ideal saltiness of your aquarium:

Saltwater aquarium saltiness: 35 ppt

Freshwater aquarium saltiness: 0.5 ppt or less

Brackish aquarium saltiness: 0.5 to 30 ppt (Depends on your fish)

 Measuring Saltiness of your Aquarium

As I mentioned above, the following are the three most commonly used devices to measure the saltiness of your aquarium:


It measures the density of water, which in seawater is a role of 3 things namely, temperature, pressure and the dissolved salt present in the water.

The density of seawater is expressed as specific gravity, and it is measured by comparing the water in your aquarium and to the seawater.

Due to the higher gravity of seawater, it is denser than the freshwater.

Although you can ignore the pressure on specific gravity while measuring, the temperature of the water cannot be kept aside.

A problem with the hydrometers is they are functional under a specific temperature, i.e. around 20⁰C / 68⁰F.

Well, the good news is buying a hydrometer will not be much of a burden on your budget, as it is comparatively cheap.

However, the results are not always accurate.

If you just have fish in your aquarium, then it is a right choice.

But if your aquarium contains corals, plants and critters, which are highly sensitive to changes in saltiness, then you should look over the hydrometer.

 2. Refractometer

It measures the refractive index of water, which varies with the mix of dissolved salts.

An advantage of a refractometer on hydrometer is that it self corrects for temperature.

Although they will provide you with a more accurate result, they are comparatively expensive then hydrometers.

Occasionally they require calibration and will have to set their point to zero, and you will have to clean them up after using.

Luckily, if you are willing to pay a higher price, then you can also get digital options that are easy to use.

Best Refractometer for Accurate Results

Vee Gee Scientific STX-3 Handheld Refractometer

This is an amazing product that is highly accurate.

The refractometer may be a little on the pricier side, but it is defiantly worth every penny.

You get measurements instantaneously and is excellent for anyone who wants to maintain the salinity of his or her fish tank.

The product is easy to use as well as easy to hold.

It comes with an instructional manual that can help you better understand the product and how to use it.


  • Accurate
  • Quick Reading


  • Expensive

 3. Electronic salinity meter

This is a digital meter which measures the saltiness of your aquarium by the conductivity of salt water.

Besides, the higher the concentrated solution higher the electricity is conducted, then converting this into the saltiness of your aquarium.

Well if you are accuracy conscious, then the good news for you is that it provides accurate results compared to the other two equipment.

So here comes the bad part: electronic salinity meter does not come cheap when compared to hydrometer and refractometer, and it’s not very easily accessible.

How Often Should You Check Salinity of Fish Tank?

The maintenance of an aquarium is not a one-time thing.

You need to continually check the water parameters for your fish to provide your fish with an optimum environment.

The same goes for checking your aquarium water for saltiness.

The best thing:

Check the saltiness of your fish tank every time you conduct a water change.

This is really important.

The water that you add to the aquarium obviously has different water chemistry as compared to the water your fish tank already holds.

Most of us just add salt to pure water.

But, there is no way of knowing if you have added the appropriate amount of salt without testing it.

So always test the salinity of your new mix and then compare it to the tank water.

Make adjustments if needed.

The goal here is to bring the saltiness of your mix as close as you can to the water chemistry of your fish tank.


This is not the only time that you should check the saltiness of your fish tank.

You should check the salinity of your aquarium from time to time, just to make sure that everything is as it should be.

How to Maintain Stable Salinity in Saltwater Tank?

Maintaining the salinity of your fish tank is a little tricky.

This is because there are many things that you need to look out for.


A plethora of factors is usually at work, undermining your vigorous efforts.

Here is how you can keep them in check.

Check for Salt Creep

Salt Creep is actually one of the significant factors that have a drastic influence on the salinity of your aquarium.

In this condition, crusty specs of salt begin to accumulate on the surface of the fish tank, the power cords, the cover as well as the decorations.


The salt creep will lead to salt deficiencies in your fish tank, as a result of which you will need to continually add small amounts of sea salt into your fish tank.

This will help you bridge the gap.

Add the Appropriate Amount of Salt

I have discussed this before in this article, but due to its high importance, this needs to be mentioned again.

When you conduct a water change, you need to match the salinity of the new water you are about to add, with the salinity of the water that is already in the tank.

Testing the new water will help you achieve your desired result.


Never test the new water right after you have added salt to it.

Let the salt mix breathe overnight and then test it again before using it.

The reading will always be a little different after you have allowed the salt to settle in and stabilize the mix.

Then you should compare your salt mix with your tank and make any necessary adjustments.

Only Top Off Your Aquarium with Freshwater

Just like in nature, your aquarium loses water via evaporation.


Only the water evaporates, leaving the salt behind.

This increases the salinity level of the remaining water.

If you top off your aquarium with saltwater, u will just end up increasing the salinity of your tank.

Hence, it is best to top off your fish tank using freshwater.

This will help you maintain the salinity of your fish tank.


You should always add freshwater that is equal in amount to the water that was lost via evaporation.

No more, no less.

You can mark your aquarium in other to keep track of the water level.

Some people use masking tape on the sump of each system.

You should top off your aquarium daily, as the longer, you wait, the worse it will get.

Related Questions

Can I put table salt in my fish tank? Table salt is not the best option. It contains additives that are highly dangerous for fish.

Should I add salt to my freshwater aquarium? You should only add a minimal amount of salt into your freshwater aquariums — about half a tablespoon per gallon of aquarium water.

Related Articles

Other Sources

Leave a Comment