Keeping tabs on your salinity is important to successfully maintain a brackish water or saltwater aquarium. Salinity is the measure of dissolved salts in water for those who don’t know. Brackish water and saltwater aquariums require a specific range of dissolved salts. Brackish water environments have specific gravity levels between 1.005 and 1.012. Saltwater aquariums can have specific gravity ranges between 1.023 and 1.028 sg. However, saltwater aquariums are usually kept between 1.024 and 1.026 sg.
There are many different tools available to measure salinity, and of course, everyone has their opinion on which is best to use. This list is not a “best salinity reader” article, but instead, it will provide a list of different salinity reading tools and discuss some of the pros and cons of each.
1. Hydrometer
Let’s start with the tool that everyone is usually first introduced to, the hydrometer. There are different kinds of hydrometers, The most common type of aquarium hydrometer requires you to pour water into the device and a swinging arm moves to where the specific gravity/salinity level is. A good example of this is the Hygger Salinity Tester. It’s a fairly straightforward device, and can generally provide you with an accurate salinity reading.
Pros of Swinging Arm Hydrometer
One of the pros of this device is that it is incredibly cheap. For example, the Hygger Salinity Tester is only $9.99. It can test any type of aquarium from freshwater, brackish water, and saltwater, and it has both specific gravity and salinity readings.
Cons of Swinging Arm Hydrometer
First, this device is very sensitive to temperature. Many are calibrated to work best at a specific temperature. You have to check what temperature your hydrometer is calibrated to and match that temperature to get an accurate reading. I have also read that the readings may become inaccurate because of salt crystal build-up on the device if it is not properly cleaned after use. Be sure to clean the device with RO water thoroughly after every use.
Floating Hydrometer
Floating hydrometers are next on the list. A great example of a floating hydrometer is the Tropic Marin – High Precision Hydrometer. This one is even easier to use than the swinging arm hydrometer. It is made out of glass, with a scale at the top that shows different levels of specific gravity. You simply drop it into your aquarium, bucket, etc., and the device will rise or drop depending on the amount of salt in the aquarium. The specific gravity is where the scale meets the water. The Tropic Marin – High Precision Hydrometer has a scale of 1.021 – 1.031, so it will only work for saltwater aquariums.
Pros of Floating Hydrometer
One of the perks of this device is that it is very simple to use. All you need to do is drop it into your aquarium, a bucket, a graduated cylinder, or anything else that will allow you to read off the scale. There is also zero calibration needed.
Cons of Floating Hydrometer
This device is fairly fragile because it is made out of glass. If not properly handled, it can easily hit something and break. It also is calibrated to work best at 77°F. It is important to match this temperature to get proper readings. You may have to clean the device thoroughly with RO water from time to time. Salt crystals can form on the glass and weigh it down, which can give false readings. Lastly, this device needs very calm water to provide an accurate reading, otherwise, it will bob and move around and will likely provide inaccurate results.
2. Refractometer
There are two different kinds of refractometers we will discuss in this article. An analog refractometer, which requires you to look through a lens to get your salinity reading, and a digital refractometer which has a screen that displays the salinity level before your eyes. Both are great tools to use, analog refractometers are usually what hobbyists move to from swinging arm hydrometers, but digital refractometers are great for anyone who just can’t see those little numbers well.
Analog Refractometer
Just a few years ago, it seemed like many analog refractometers cost an arm and a leg. Now, the price has gone down significantly and you can pick one up for around 16$ – 20$. The Agriculture Solutions Store has Salinity Refractometers on sale for $18.99, which is much better than the prices many years ago.
The device is fairly easy to use, First, you must calibrate the device to “0”. Use distilled water or RO water to do this. Simply place a few drops of distilled water on the blue prism, and use the provided screwdriver to turn the calibration screw until it reaches “0”. There should be instructions that take you through this process in the box.
Once calibrated, wipe the prism to remove the distilled water. Once you do that, you can place your saltwater on the prism to test your salinity and/or specific gravity.
Pros of Analog Refractomers
Once calibrated, this refractometer is very accurate. You may need to check its accuracy from time to time, but it should bode you well for a few months without re-calibration. I use analog refractometers as my go-to salinity checker. The one linked above also provides automatic temperature compensation (ATC). This pretty much means that you don’t have to worry about the temperature of the water to get accurate salinity readings.
Cons of Analog Refractometers
The biggest con of this device is that it may be harder to see the numbers when looking through the lens for anyone people with vision impairments. Also, now you have to remember to keep an eye on the calibration of the device. Over time, it may need to be re-calibrated, and if you forget, your salinity levels may be higher or lower than usual.
Digital Refractometer
Digital refractometers are similar to analog refractometers, in the way that you place water on a prism. However, a digital refractometer uses an LED to determine the amount of refraction occurring, or the angle of refraction. The bend in light due to the particles suspended in water will determine the salinity/specific gravity. A fairly popular digital refractometer is the Milwaukee MA887. The link provided will take you to its Amazon store page. You can also go into a deep dive into all its components and how it works by checking out the Milwaukee MA887 manual.
Pros of Digital Refractometer
One of the biggest pros of this device is its ease of use. You don’t have to look through lenses or try to determine where the salinity line falls under. You simply place your water on the prism and let the device do the rest. The Milwaukee MA887 will give you results in around 1.5 seconds. On top of that, you will get results in specific gravity, salinity, or practical salinity unit (PSU).
Cons of Digital Refractometer
This thing is expensive, and not many of us are ready to dish out $100+ for a device that reads salt levels. Also, from my understanding, this device isn’t perfect in regards to accuracy. If we are specifically looking at the Milwaukee MA887, it has an accuracy range of +/- .002. If that’s true, then you may get results of 1.026, but in reality, your salt content could be sitting at either 1.024 or 1.026 sg.
3. Conductivity Salinity Testers
Salinity can be tested with a conductivity tester. Saltwater is more conductive than freshwater. The more minerals there is in water, the more conductive it will be. Saltwater has a lot of dissolved salt, which makes it more conductive. The Hanna Salinity Tester (HI98319) is a perfect example of a tool that uses conductivity to determine salinity, PSU, or specific gravity of your aquarium water. There are many other types of conductivity tools out there, but after doing some research, this one is fairly popular.
Pros of Conductivity Testers
Speaking specifically about the Hanna Salinity Tester, the machine is very easy to use. You can go into detail on how it works, by checking out the Hanna Salinity Tester manual. Once calibrated, all you’ll have to do is dip the tester into your aquarium to get a reading. Another pro of this device is that it will also provide you with a temperature reading of your aquarium.
Cons of Conductivity Testers
Not everyone wants to think about calibrating their devices. The Hanna Salinity Tester will also need re-calibration from time to time. Hanna Instruments makes it a little easier, with their 35 PPT Salinity Calibration Solution (HI70024P). You can read through the manual to see how to properly calibrate this device. Also, this device is a little more expensive compared to hydrometers or manual refractometers, but the work it puts in could make it worthwhile.
Final Notes
Finding the perfect salinity tester is up for debate. What works great for some, may not work well for others. Whether a hydrometer or refractometer is more accurate, is completely dependent on the person using it. All these tools work well, but some may be better for an individual than others. If I had to choose two products from this list to add to my arsenal, I would pick the Topic Marin Floating Hydrometer and Hanna Salinity Tester. I love the ease of use of the Topic Marin Hydrometer, and I think it’s a great idea to use conductivity to determine salinity levels with the Hanna Salinity Tester. If you have a personal favorite tool that you use to test your salinity, don’t hesitate to share your experience! Check out more aquarium resources to continue your fishkeeping journey!