Anyone who keeps a saltwater aquarium, or is planning to, will know that they require above all the correct amount of salt in their water at all times. We recently reviewed the best refractometers for saltwater aquariums and show the results below. This is our latest 2020 refractometer review.
The wrong salt dilutions can be incredibly detrimental to not only the corals and plants in your aquarium but also to your fish too.
The above means that you need a way to measure and keep a careful eye on your aquariums saltwater, and what better way to do this than by using a refractometer? But which one to choose, considering there is a myriad of them available out there? Which are the best refractometers for saltwater aquariums?
What Is A Refractometer?
A refractometer is a tool that is used to measure the concentration of aqueous solutions. It is also used throughout the food, agricultural, and chemical industries, as well as in the saltwater aquarium keeping hobby.
To understand the refractometer correctly you will need to go back to your school science classes, as it will have been here you would have learned about refraction. This is when, as a reminder, light changes its direction as it enters a liquid, or in other words, bends. Refractometers measure the degree to which the direction of this light changes allowing you to determine the concentration of solutions.
A quick look at the 5 Refractometers tested
Why Do You Need A Refractometer?
As you may know or might be about to discover, saltwater aquariums can be a lot of hard work. You are about to spend an awful lot of time getting and keeping your aquarium right. This includes the frequent and often large task of mixing the saltwater correctly. An activity that really is an art and you won’t want to get wrong.
Getting the mix of your saltwater wrong can be detrimental. Salinity levels that are too low or too high will have a negative effect on your aquarium’s inhabitants. Stress is an extremely likely result of this which could in some extreme cases even lead to death.
The above is why measuring the salinity in your saltwater is vital to the successful running of your aquarium, and a refractometer is the best tool to help you with this. It will ensure that your water parameters are correct and stable leading to happy and healthy fish.
TOP 3 Refractometers Reviewed
Professional Automatic Temperature Compensation Salinity Refractometer for Aquariums, Marine Monitoring, Saltwater Testing.Dual Sacle: 0-100ppt & 1.000-1.070 Specific Gravity
- Upgraded Quality
- Partable Hard Storage Box
- Dual Salinity Scale
- Automatic Temperature Compensation
- Full 12 Month Replacement Warranty
Magnum Temperature Salinity Refractometer
Designed for the measurement of seawater, the Magnum Salinity Refractometer is a precise optical instrument for checking the salinity in your water. It is capable of measuring on two parts, both specific gravity and parts per thousand, and has automatic temperature compensation (ATC) as well as being dual scale and incredibly portable.
Relative to other brands which are twice the price the Magnum Salinity Refractometer performs very well in my opinion and was fairly simple to use. I did, however, struggle to see through the eyepiece without my glasses, and even with them found it a little awkward. Calibrating the device was quick and easy enough for a child to perform, but I have found that this needs doing on a regular basis.
Milwaukee MA887 Digital Salinity Refractometer with Automatic Temperature Compensation, Yellow LED, 0 to 50 PSU, +/-2 PSU Accuracy, 1 PSU Resolution
$108.30 in stock
5 used from $95.30
- Laboratory tested
- Yellow led display
It would be more than fair to say that the Milwaukee Refractometer is exactly what it claims to be; an accurate refractometer. It is also incredibly durable, runs a small ‘self-check’ on being switched on, and gives the confidence one needs in a product such as this. The digital display is easy to see, even if you wear glasses and don’t have them on, and the salinity is measured in three ways.
On the downside, I did find that this refractometer needed calibrating before every use, but since this is simple to do it is not much of a problem. The unit is also, perhaps for some, a little on the pricey side but I would say worth every cent.
Vee Gee Scientific STX-3 Handheld Refractometer, with Salinity Scale, 0-100, +/-1.0 Accuracy, 1.0 Resolution
$104.15 in stock
- Handheld portable refractometer for measurement of salt concentration in parts per thousand (PPT) (0 to 100%) and specific gravity (SG) (1.000 to 1.070) of seawater in the 10 to 30 degrees C temperature range
- Automatic temperature compensation (ATC) for immediate and accurate calibration readings, regardless of ambient temperature
- Ambient light illuminates the scale; no additional power source is required
- Durable metal and rubber outer shell with a telescope-shaped, streamlined design (40 x 40 x 185mm), a rubber grip to guard against hand heat for accurate measurements, and a non-roll stand to protect against damage
- Optical glass prism mounted in all-metal housing for quick temperature equilibrium between sample and prism
Vee Gee Scientific Tester
The Vee Gee Scientific tester is truly a refractometer that you can trust in. It very rarely needs recalibration and is most accurate at every use. It has automatic temperature compensation and handy ambient light that illuminates the scale. Plus it is made of durable materials and incredibly comfortable to hold.
It has to be said, however, that of all the units we tested this one was the hardest to calibrate correctly. A downside that, perhaps, is not much of an issue since it only needs doing on an infrequent basis. The bag that it comes in is also not of the best quality, but since this has no effect whatsoever on the working of this refractometer it is of little to no consequence.
Refractometer vs Hydrometer – Which Is Best?
Only a couple of decades ago most saltwater aquarium keepers would have managed salinity levels in their water with a hydrometer. These were easy to use by simply placing the unit into the water, and then allowing it to fill. Once full, the hydrometer is then removed from the aquarium and placed on a level surface, where the swing arm would indicate specific gravity.
Though simple, the hydrometer, however, is not without its limitations. Bubbles, for example, could easily get stuck to the swinging arm of the device and cause inaccurate readings. Moving parts also would degrade over time, and they have no function to adjust the temperature. As the water cools or warms, you see, it becomes less dense or denser respectively affecting the hydrometers readings.
By comparison, the refractometer is much more accurate. Many units can and do automatically correct themselves for temperature differences giving a much more reliable reading. It also does not measure the density of the water directly but rather measures how the light is bent through the liquid also improving on the result.
However, the refractometer does have at least one downfall in that compared to the hydrometer it is rather more expensive. On average a hydrometer will cost around $10 whilst refractometers range from $20 to $100 plus.
How To Use A Refractometer
Before you can use your refractometer you will need to ensure that it is calibrated correctly. You can use either salinity calibration fluid to do this or RO/DI water. This process should also be repeated periodically in order to ensure your refractometer remains reliable.
How to use your refractometer will depend upon which type you have opted to buy. Following are the instructions for the use of both:
Refractometer With Eye Piece
- Place a few drops of your saltwater mix on to the glass pane of your refractometer.
- Place the clear cover of the refractometer over your water sample.
- Point your refractometer at a source of bright light such as your aquarium or a lamp.
- Look through the eyepiece in the back of your refractometer to obtain the reading.
- Your reading is the point where the colored half of the viewfinder stops.
- Simply drop a sample of your saltwater mix into the test well on your digital unit and it will display the reading back to you of the salinity of the water.
Please note, digital refractometers can provide readings in the newer standard Practical Salinity Units (PSU), as well as PPT and S.G.
What Is SG (Specific Gravity)
Specific Gravity (SG) is the ratio of the density of any substance to the density of another substance taken as standard. In the case of aquariums, water is the standard as it is for all liquids and solids, whilst hydrogen or air, just for information, is the standard for gases.
What Should The SG Be In A Saltwater Aquarium?
Speaking in general terms it is best to aim for specific gravity (SG) in your aquarium similar to that of natural seawater. This would equate to an SG of around 1.026. It should be noted, however, that some fishkeepers who run ‘fish-only’ aquariums prefer to keep their SG slightly lower, 1.022 SG is the norm.
Also to be taken into account is that specific gravity (SG) will vary from ocean to ocean and hence fish species to species. You should always research a fish species requirements before adding them to any aquarium that may not have a suitable SG.
What To Look Out For When Buying One
When buying a refractometer there are three main features you should be looking out for. These are:
- That your refractometer is definitely one that can be used to measure salinity. There is a wide range of refractometers on the market but not all are for this purpose. Some are used for blood, urine, wine, honey, antifreeze, and beer, and definitely not suitable for your tank.
- Following on from point one it is also fair to say that not all salinity refractometers are created equal. You see, the majority of salinity refractometers are designed to measure amounts of sodium chloride (NaCl or salt) rather than seawater. Seawater, perhaps surprisingly, contains more than just sodium chloride; it also has magnesium and calcium meaning a seawater refractometer rather than a saltwater one is preferable.
- Also, as we mentioned earlier automatic temperature compensation (ATC) is incredibly beneficial to a saltwater aquarium refractometer. This is due to water warming up and cooling and becoming more or less dense respectively. This, as we also learned earlier, can have a detrimental effect on readings and should be avoided where possible.
Where To Buy One
There is a wide variety of places that you could purchase a refractometer from. These include your local aquatic store, pet store, or online from websites such as Amazon and Chewy.com. In our opinion, however, online sources are always the easiest places to buy from as well as being the ones with the most variety.
Quick Recap on the Best 3 Refractometers
- Can You Mix Saltwater In The Aquarium? Yes, providing it is the first filling of the tank and there are no fish in it. However, once fish are added saltwater should be mixed before adding it to prevent problems from occurring.
- Are Refractometers Accurate? Absolutely! However, those most accurate have automatic temperature compensation (ATC) and measure seawater rather than saltwater salinity.
- What Is The Correct Salinity For A Saltwater Aquarium? The recommended level is around 1.026 SG, but anywhere from 1.022 to 1.027 SG is perfectly acceptable.
- How Does A Refractometer Measure Salinity? By measuring the change in direction, or bending of the light, as it passes from air to water.
Conclusion: Best Refractometers For Saltwater Aquariums – Results
No doubt you will now be raring to get yourself a refractometer as soon as possible, and asking which one of our top three is the ultimate choice? Well, that would an incredibly hard choice to make, however, if pushed, we would select the Magnum Temperature Salinity Refractometer.
With its automatic temperature compensation, dual scales, portability, and ease of use, the Magnum Refractometer stands out in a crowd. It also does not hurt that this selection is the least expensive of the options, but certainly not of lesser quality.
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