HomeAquarium ReviewsThe Best Hydrometer for Saltwater Tank in 2023

The Best Hydrometer for Saltwater Tank in 2023

If you have a saltwater aquarium, you need a quality hydrometer. This tool is useful as you can use it to monitor the salinity of the water. The best hydrometer for a saltwater tank can help ensure that the water does not get too much or too little salt as this will be bad for your fish.

Saltwater aquariums are quite sensitive, making it necessary to keep a delicate balance of salinity. The water should have just the right amount of salt in it and a hydrometer can make that possible.

Although filters, heaters, and other paraphernalia are important, you should also invest in the hydrometer. This device measures the amount of salt dissolved in your aquarium’s water to tell if the salinity is too low or if it went up too much.

The salinity of the water also increases when too much of it has evaporated. This means you will need to add more freshwater into the mix. You may also be wondering if you need a hydrometer for a freshwater aquarium.

The answer is no because this device measures salinity and there is hardly any salt in freshwater tanks. Even if there is a bit of salinity, it will not do anything to freshwater fish. This article National Park Aquarium will teach you how to find the right product that you should use in your tank to maintain your fish’s health and well-being.

Best Hydrometer for Saltwater Tank Reviews

1. Agriculture Solutions Seawater Salinity Refractometer

Agriculture solutions seawater salinity refractometer
Agriculture solutions seawater salinity refractometer

Although this is a relatively simple device, you can get accurate readings. The nice thing about refractometers like this is that you can get two readings from 2 different scales, namely the parts per thousand and specific gravity. This hydrometer for a saltwater aquarium provides you with more data to figure out your tank’s overall health.

The thing with hydrometers is that you need to take the water’s temperature into account when taking measurements, more so when using a refractometer. Fortunately, this product has automatic temperature compensation. It provides more accurate readings, which is important in maintaining proper water chemistry.

Another nice thing about this device is how hefty it feels when you hold it. You can tell that it is from durable and quality materials. Also, because it is an analog device, there are no electric or moving parts that might get damaged by wear and tear.

You can expect it to last for at least a couple of years – that is if you do not drop it and cause any serious damage to it.

Another advantage is that there is no need for batteries. It is also easy to calibrate. It just takes a couple of steps and you don’t need to do it again for a very long time. However, you have to clean it thoroughly after every use to prevent mineral deposits.

Now, here is the problem. It is not a calibrated refractometer out of the box and you need to buy the calibrating kit separately. This means if you did not buy the kit at the same time as the hydrometer, you would not be able to use the device immediately. It would have been better if the kit was already included in the package.

  • Provides data from two scales
  • Comes with automatic temperature compensation
  • Made from durable materials
  • Easy to use and calibrate – It does not need any batteries.
  • Provides accurate readings
  • Does not come with a calibration fluid
  • The scales are kind of hard to read

This product is a reliable and quite accurate refractometer. Although it is an analog device, you will be getting an accurate method of measuring the salinity of your aquarium. Even if you have not used it before, you will get the hang of it after a bit of practice. This hydrometer will help you better take care of your marine aquarium.

2. Coralife Hydrometers

Coralife hydrometers
Coralife hydrometers

Once you figure out how to use this hydrometer for a fish tank properly, you will find just how easy it is. Some people think that you need to be a chemist to use a hydrometer, but it is not true.

You just need to fill up this device with water from your aquarium and then wait for the needle to settle. Once done, you can get an accurate reading. Take note that you need to place this on a level surface to gain the most accurate reading.

Speaking of accuracy, it is the same brand that most professional and experienced aquarium keepers use, so you will be in good company. The reason why this is such a trusted brand is the high level of precision.

It is highly precise when it comes to measuring the salinity of saltwater aquariums. This is important because saltwater fish are quite sensitive to changes in water chemistry. Even a subtle change in salinity can have adverse effects.

Another neat thing about this tool is that you can get readings in two different scales, namely parts per thousand and specific gravity. In other words, you can get the salinity using different methods, depending on what you are more familiar with.

It is also great that this hydrometer can work with brackish water. It does not do anything to skew the results whatsoever. As with any other hydrometer, you have to wait 24 hours to get an accurate reading.

It is also nice that you do not have to wait even longer before you can start measuring. However, you have to wash it thoroughly after using it in brackish water to prevent mineral deposits.

The problem with this product is that the instructions are quite hard to understand. If you haven’t used it before, relying on the included directions to learn will not take you anywhere. It is like the writer’s first language is not English. It is better to search for online videos on the subject. You will learn easier as it will show you what to do exactly.

  • Easy to use and read
  • Provides accurate values
  • Gives readings on two different scales
  • Can work with brackish water
  • Comes with a bubble remover for more accurate results
  • The provided instructions are unclear
  • You will have to wait around 24 hours before reading

This is a simple device that does not have any digital components while still providing accurate readings. It is a simple and reliable way to monitor the health of your saltwater aquarium. You do not need to spend a lot of money while still saving yourself hundreds of dollars in marine fish and veterinary services.

3. AUTOUTLET Salinity Refractometer

autoutlet salinity refractometer
Autoutlet salinity refractometer

Whether you like using specific gravity or parts per thousand, you can compute the salinity of the water with this device. What’s even better about this refractometer is that you will have more data to work with. You can get a more accurate reading with such data, and you can compare the results of different computation methods.

This device is also quite easy to use. Just use a couple of drops of the sample water in the hydrometer. There is no need to use other chemicals. You can get your results in just a couple of minutes. However, even though it provides quick results, it does not mean it is not accurate.

Out of the box, this is not yet a calibrated hydrometer. You do not have to worry, though, as you will have an easier time calibrating it. The only thing you need would be a couple of drops of calibrating fluid to get a high level of accuracy. The best part is that you do not have to recalibrate for many years.

You just need to hold this device in your hand and you can easily tell that it consists of only the most durable materials. The manufacturers also assembled it with longevity in mind. Because there are no moving parts, wear and tear should not be an issue. What this means is that this would be the last hydrometer that you will need to buy.

Now, the issue that I have with this product is that it does not come with a calibration kit. Yes, it says that you can use distilled water, but it will be a lot more accurate if you used the actual calibration fluid, which did not come with the kit. You have to order it separately, therefore, you cannot calibrate the device immediately out of the box.

  • Provides readings in both specific gravity and thousandths
  • Easy to use
  • Easy and quick to calibrate – It only takes a couple of minutes
  • Made from durable materials
  • Automatically compensates for the ambient temperature
  • You will have to purchase the calibrating fluid separately
  • The focal part of the eyepiece is a bit loose

This is a great tool that you can use if you are not that technically inclined. There are no buttons to push, nor are there any screens with lots of numbers on them. Just place a couple of drops of the tank water, and then take your reading.

4. Instant Ocean SeaTest Hydrometers

instant ocean seatest hydrometers
Instant ocean seatest hydrometers

This item might seem like a simple piece of plastic but this is actually a precise instrument. You can get a reading that is accurate up to the thousandth, which is important when you are dealing with the salinity of a saltwater aquarium.

Marine fish are quite sensitive to changes in water chemistry. With the help of this item, you can keep abreast of the condition of the water.

If you are like me and already have trouble reading the ingredients list of most groceries, you would like the big numbers on this device. There are clear markings on the scale and the numbers are big and easy to read.

Another nice thing about using a hydrometer like this is that you do not need to use other tools to get a reading. Just put tank water in the reservoir and then wait for the needle to settle.

Speaking of taking a reading, you will sometimes need to wait a couple of hours, sometimes even overnight. This item is great because it has such a wide base that prevents the instrument from shaking, which could cause bubbles to form and skew the readings. This item’s wide base prevents all of these from happening.

I do have an issue with this device, though, and that is it uses very fragile plastic for its material. I had two of these hydrometers. When I accidentally dropped one, it cracked easily, rendering it useless. It is a good thing that these devices are quite cheap, so I just bought a new one.

  • Accurate up to the thousandths
  • Easy to read – It has clear scale markings with safe zones
  • Easy to use – There is no need to use any additional tools
  • Has a stable base
  • Cheap, yet effective
  • A bit fragile
  • Bubbles are hard to remove inside the hydrometer

You do not need to spend a lot of money just to keep your saltwater aquarium in top shape. This simple hydrometer might be quite cheap but it helps monitor the health of the aquarium’s water. You already spent hundreds of dollars on a saltwater tank and you can help protect it by spending a couple of dollars more.

5. ORAPXI Digital Salinity Tester

orapxi digital salinity tester
Orapxi digital salinity tester

This device can provide you with a lot of different kinds of data at once. Aside from getting the salinity, you will also receive other bits of info like the water’s temperature. You can get a lot of data as fast as possible. Compared to regular hydrometers, you can get your needed information in just seconds.

Unlike analog hydrometers, you will also get to use an easy-to-read, backlit, LED screen. You do not need to squint to figure out where the needle is pointing. You can just read the numbers on the screen. This is the easiest way to monitor the salinity of your tank closely.

Another thing that I liked about this product is that you do not even need to get your hands wet. Other hydrometers need to be dipped into the tank to fill it up with water, which can get quite messy. This device only needs you to put a bit of water in a cup and then dip the end into it.

This hydrometer also knows that it needs to compensate for the temperature of the water and the ambient temperature. You no longer have to do the computations yourself because this device already has a built-in thermometer and it automatically compensates to provide you with the correct value.

One downside I noticed in this device is that it does not provide specific gravity values. Although you can still use the ppt numbers provided by this digital hydrometer, it would have been better if it also provides the specific gravity.

Moreover, this device is quite confusing to calibrate. You have to search online for a tutorial on how to do it because the included instructions are unclear.

  • You get a lot of different data fast
  • Easy to use and read
  • Not messy to use – You do not have to wet your hands
  • Provides a lot of accurate data
  • Automatically compensates for ambient temperature
  • Does not give specific gravity values
  • A bit confusing to calibrate

This device is one of the easiest ways to monitor the salinity of your aquarium. In addition, it is significantly quicker than any analog method. You can get an accurate reading in just a couple of seconds. Compare that with most analog hydrometers where you need to wait at least a couple of minutes before you can start taking readings.

Factors to Consider When Choosing Hydrometer for Saltwater Tank

hydrometer for freshwater aquarium
Hydrometer for freshwater aquarium

Here’s the thing about hydrometers: they are not that expensive. You do not have to spend a lot of money to get a good quality hydrometer. However, you should keep in mind the importance of finding one that works well. Here are a couple of things to keep an eye out for when shopping for hydrometers:

1. Ease of Use

Not everyone is technically-inclined, so choose a hydrometer that is easy to use. Fortunately, most hydrometers in the market are quite easy to use. It only involves dunking the device into the water. However, choose one that is easy to read. This means those with clearly printed scales and numbers.

2. Accuracy

Accuracy is the most important factor when choosing a hydrometer. Here’s the tricky part. How do you know if a hydrometer is accurate or not? To figure out if a hydrometer is accurate, fill it with distilled or pure water. The reading should be zero. Any other result means that the hydrometer is not accurate at all.

3. Safety

The materials used for making the hydrometer should not be harmful to your fish. Check if the hydrometer contains plastics known to leach toxic chemicals when exposed to water. These toxins may not cause immediate discomfort or harm, but they build up over time until there is enough to become dangerous.

4. Wide Usage

The hydrometer should not just be good for saltwater. Ideally, the hydrometer should also be usable for brackish water. In other words, the hydrometer should have scales that show both specific gravity and salinity.

5. Analog or Digital?

Although the majority of the hydrometers in the market are analog ones, you can also find many digital devices. A clear advantage of digital hydrometers is that they are easier to read.

There is no need to judge where the needle is pointing and you will receive an accurate reading. Moreover, digital hydrometers deliver results faster. Note, though, that they are also quite expensive. They often cost many times more than analog plastic ones.

Depending on how you use them, you can still get an accurate reading from the plastic hydrometer. Choosing one over the other will mostly depend on convenience.

6. Easy to Clean and Maintain

Clean your hydrometer after every use to ensure accuracy. This means you have to find a hydrometer that is easy to clean. Choose the ones that are easy to clean using regular cleaning brushes.

This means there should not be too many bends. This will prevent mineral deposits from accumulating in your hydrometer.

7. Durability

A hydrometer is something that you will be using constantly when you have a saltwater tank. Pick one that could last at least a couple of years. If you are using a typical plastic hydrometer, the plastic should not be brittle. Also, plastics tend to get cloudy after a couple of months.

hydrometer for fish tank
Hydrometer for fish tank


The best hydrometer for saltwater aquarium is essential if you are keeping a saltwater tank. Marine fish and other creatures are quite sensitive about the salt content of the water in their tank. You need a hydrometer to monitor the salinity of the water and keep your fish healthy as a result.

Now that you have reached the end of this article, you already know what to look for when shopping for a hydrometer. Even though hydrometers are not that expensive, you still have to choose one that provides correct and accurate readings.

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Further Reading
Kevin Mills, the founder of Nationalparkaquarium.org


-- Founder --

I'm Kevin Mills, the founder of Nationalparkaquarium.org, where I share my deep passion for aquariums and aquatic life. With over 20 years of experience in fishkeeping, covering everything from tending to saltwater and freshwater tanks.

Kathleen Wood


-- Interrogator --

Kathleen Wood, a seasoned marine biologist, possesses a wealth of knowledge and experience in her field. Her research on tropical fish biodiversity spans over three decades, and she has contributed numerous scientific papers on aquatic life.