10 Best Aquarium Hydrometers

17412 Reviews Scanned Last Updated: Aug 6, 2020

#1 Refractometer Fishkeeping Automatic Temperature Compensation

Be sure to buy a calibration solution and test it before use! When I received it, I tested it with distilled water, and it seemed dead, but my salinity reading in the aquarium seemed too high as I expected. So I bought a calibration test solution, which shows that the refractometer needs to be clearly adjusted. Once I adjusted the refractometer, my aquarium salinity reading reached the expected 1.026. I have it independently tested and the refractometer now reads dead and validated tests. Now that it's calibrated, I like it!

  • Description:Salinity Refractometer for Seawater and Marine Fishkeeping Aquarium 0-100 PPT with Automatic Temperature Compensation
  • Brand:Agriculture Solutions
  • Product Dimensions:2 x 3 x 8 inches ; 8.8 ounces


  • Measure 2 scales, specific gravity (D 20 to 20) and a few thousandths.
  • Measuring the salinity of salt water or water is an ideal choice for aquariums and ocean monitoring.
  • The main body is made of chromium and is very durable.
  • It has the function of automatic temperature compensation.
  • Equipped with hard shell, eyedropper, screwdriver, user manual and cleaning cloth.

#2 Exo Terra PT2466 Hygrometer

These seem to be correct. I solidify plant materials in Mason cans and use 62% Boveda bags. I got four of them, and all four died at 62%. The best part is that they are just right for the jar, because I put them in a transparent jar, and these little guys are right in there, and I can monitor the humidity without opening the jar. They have a circular foam sticker affixed to the back of the device, but if you pop up the small circle in the middle, you can use the piece of the double-sided sticker to paste it inside the glass facing out. They achieved my desired purpose perfectly.

  • Description:Exo Terra Terrarium Hydrometer
  • Brand:Exo Terra
  • Product Dimensions:0.5 x 4.1 x 7 inches


  • Analog hygrometer
  • Wipe it clean
  • Very suitable for monitoring humidity levels
  • Stick the hygrometer in the aquaculture box
  • Easy to read and install
  • A clear display of the analog dial

#3 Coralife Energy Savers ACLAF877 Hydrometer

Easy to use and seems to work. Whether it is really accurate is unknown to me, because I am not familiar with salt water. I use it to create water conditions for Amano Zoo. Some of the things you need to know when using this is that the manual says you should keep it with salt water for 24 hours before doing the actual test. Similarly, once it is ready for testing, you should slap the bottom to a soft part of the floor, not a hard place. From YouTube, it seems to make the dial move correctly, otherwise the dial will rise in a straight line.

  • Description:Coralife Energy Savers ACLAF877 Deep Six Hydrometer
  • Brand:Coralife
  • Product Dimensions:6.7 x 0.8 x 4.7 inches ; 3.2 ounces


  • Cora Life is one of the leading manufacturers of high-quality aquarium products in the market.
  • Included components: all components contained in pictures and descriptions
  • The hydrometer is easy to read and accurate and can provide temperature correction readings in warm water aquariums.
  • Coralife's hydrometer collects real water samples at a depth of 6 inches.
  • Coralife is one of the leading manufacturers of high-quality aquarium products in the market.
  • Cora Life's hydrometer collects real water samples at a depth of 6 inches.

#4 RZ Refractometer Professional Monitoring 1 000 1 070

The window is easy to read and calibrated (check against calibration fluid). It is much lighter than my old refractometer (Sybon brand). I don't know if it's positive or negative, it's just different. I think it feels cheaper than mine, but I don't know if it really means anything, or if it's just a different material, so I'm not going to pick a star for it.

  • Description:RZ Salinity Refractometer for Aquariums, Seawater, Marine Fish-Keeping, Testing, Salt Water Tester with ATC, Specific Gravity Salinity Meter with Dual Scales 0-100ppt & 1.000-1.070
  • Brand:RZ


  • Dual scale: salinity refractometer density specific gravity (D 20 beat 20) 1.000 parts per million-1.070SG (0.001), concentration measurement range 0-100ppt, minimum reading 1 ‰ (1 ‰ = 1ppt=1000ppm)
  • Easy to use: the salinity refractometer is easy to operate and only needs 2 to 3 drops after calibration to get accurate reading, replacing the shortcomings of poor quality and difficult reading of your refractometer.
  • Salinity meter: measure the salinity of salt water or water, suitable for aquariums, sea water, marine fish culture, seawater fish tanks, saltwater ponds, hot springs and so on.
  • Durable and lightweight: the salinity meter adopts aluminum valve body and the shell is ABS rubber, which is wear-resistant and corrosion-resistant. Cover the plastic box and sponge to ensure the safety of the refractometer. If you have any problems, please feel free to contact us.
  • Automatic temperature compensation: the salt water tester can automatically compensate the temperature when the ambient temperature changes, which makes it easier and faster to obtain accurate readings.

#5 AUTOUTLET Refractometer

This salinity refractometer is easy to calibrate, and you can see the results quickly, and it's definitely worth it.

  • Description:AUTOUTLET Salinity Refractometer,Automatic Temperature Compensation Salt Water Tester Hydrometer 0-100ppt & 1.000-1.070 Specific Gravity ATC Refractometer for Sea Water Aquarium Tank, Marine Industry
  • Product Dimensions:7.9 x 3.5 x 2.4 inches ; 8.5 ounces
  • Color:Salinity Refractometer
  • Ean:0713289306953
  • Item Weight:8.5 ounces
  • Model Number:8541957195
  • Size:Salinity Refractometer
  • UNSPSC Code:41110000
  • UPC:713289306953


  • [2 scale measurement] specific gravity (D 20 amp 20) and a few thousandths replace your poor quality hydrometer, which is difficult to read.
  • [salinity refractometer] measures the salinity of salt water or water, monitors and controls the concentration of salt water and salt water, and is an ideal choice for aquariums and marine applications.
  • [density measurement range] 1.0-1.070, with a minimum scale of 0.001.
  • [concentration measuring range] 0-100 ‰, the minimum measuring range is 1 ‰.
  • [ATC] automatic temperature compensation, 0-10 °C.

#6 SunGrow Salinity Aquarium Refractometer Remarkable

I've been using plastic salinity hydrometers for years. It disturbs the fish, and it's a little messy. When it dries, the floating needle gets stuck, and I have to wet it and shake it to make it move freely. It worked (to some extent), but I felt uncomfortable because I got an accurate reading. In addition, over the years I have heard that refractometers are the best way to measure salinity. However, I am tired of pricing and think tricky calibration is necessary. This sounds like a laboratory instrument that can be picky and requires constant attention. This is true in all respects. The phone is priced slightly higher than the plastic version (about $15). The calibration process is simple-drop a few drops of RO water on the glass, close the cover, observe through the observer, and then turn the screw until the line is zero. That's it. It's even easier to use because you do the same thing with tank water, but there are no calibration steps. The whole process takes only a few seconds and is very easy to use, but you do need to lift it into brighter light to get a clear reading. There is a blue line indicating the exact level of salinity. Without speculation or estimation, I strongly recommend it to serious saltwater aquarium enthusiasts.

  • Description:SunGrow Aquarium Refractometer, 7.6 Inches, Measure Salinity of Water, Remarkable Accuracy, Includes Calibration Tool, Ensures Overall Health of Plant and Marine Life, Easy and Clear Reading
  • Brand:SunGrow


  • Automatic temperature calibration-the calibration process should be carried out in rooms and instruments at 68 °F. The refractive index of a liquid varies with temperature. Due to automatic temperature calibration, any change in ambient temperature between 50 °F-86 °F will not affect the accuracy of the reading.
  • The refractometer is designed specifically for the saltwater aquarium-the algorithm is designed to test sea water and salt water. This is different from the standard refractometer, which is not calibrated to check the salinity of aquarium water and can cause errors in your readings.
  • Keep your fish and plants in the best health-clean, pure salt water is vital to the vitality of your ocean or coral reef aquarium. Using this refractometer to measure the salinity of sea water, the target salinity of the reef pond should be 35ppt.
  • Equipped with a rugged housing, including pipettes and calibration tools-this 7.6-inch refractometer is not only well made, but also has a rugged housing to store the refractometer safely and easily when not in use. Everything you need: eyedroppers, screwdrivers, user manuals, hard shells and cleaning cloths.
  • Easy and clear readings for saltwater aquariums and coral reef tanks-the refractometer has a focal length adjustment on the eyepiece, which will make your optical system clear, clear lines and easy to read.

#7 GXSTWU Hygrometer Thermometer Temperature Terrariums

I have an 4x2x2 Zen habitat shell, so I put these in the back corner to show the hot side temperature and the low side temperature. I have a bearded dragon, so the humidity will not be very high, but they do show both temperature and humidity, which is great! My battery has been used for five or six months, and the battery is still original. They carry paper clips, and the paper clips have an adhesive square that you can paste on the back wall. These are easy to read, and they look great! 10/10

  • Description:GXSTWU Reptile Hygrometer Thermometer LCD Display Digital Reptile Tank Hygrometer Thermometer with Hook and Velcro Temperature Humidity Meter Gauge for Reptile Tanks, Terrariums, Vivarium
  • Brand:GXSTWU
  • Product Dimensions:2.1 x 0.7 x 1.3 inches ; 0.96 ounces


  • Fashion design: stylish digital vivarum thermometer with hook and nylon buckle for easy installation to any reptile tank or torpedo.
  • 100% new quality reptile tank thermometer hygrometer: accurately monitor the temperature and air humidity of aquarium, animal tank and reptile tank.
  • Quality assurance: our carefully purchased thermometer and hygrometer series are manufactured in accordance with the highest standards expected by customers. And provide 365-day warranty, if you have any quality problems, please feel free to contact us by email, we will provide you with a satisfactory solution.
  • Fahrenheit temperature conversion: press the C hand F hole on the back of the item with a paper clip. The temperature can be displayed in Fahrenheit or Celsius.
  • Extraordinary value: this accurate reptile thermometer and hygrometer allows you to monitor the temperature and humidity in the reptile tank at any time to ensure that your beloved reptile is in perfect health.

#8 Aquarium Salinity Refractometer Saltwater Tank Dual

I have been waiting for months to provide a review to ensure an honest opinion. Very accurate. Occasionally (not often a problem) the refractometer needs to be readjusted to ensure accuracy. However, I just took extra steps to always check the accuracy before the water in my aquarium changed. Feel solid and take everything you need with you to make water testing easier. If you can't get enough light from the window to get a clear reading, I would recommend a lamp. Please don't hesitate to buy.

  • Description:Aquarium Salinity Refractometer with ATC Function,Saltwater Test Kit for Seawater, Pool, Aquarium, Fish Tank.Dual Scale: Specific Gravity & Salt Percent
  • Brand:aichose
  • Product Dimensions:7 x 1.5 x 1.5 inches ; 3.68 ounces
  • Ean:0603097377590
  • Item Weight:3.70 ounces
  • Model Number:8541957181
  • UNSPSC Code:41110000
  • UPC:603097377590

#9 Salinity 100 0ppt 0 95 1 08 Measurement Saltwater

This is a clever gadget. If you accidentally drop it into the swimming pool, it will be waterproof. It's more accurate than using a cell phone, which may have taken me a lot of trouble to find out. This will save you a headache.

  • Description:Salinity & Temp Meter Pen Type Salt Water Quality Tester ATC NaCl, 9999 ppm / 100.0ppt/ 10% / 0.95-1.08 SG Measurement Units 4-in-1 Checker for Saltwater Aquarium Pond Food Pool Cooking Seawater
  • Brand:Gain Express
  • Package Dimensions:7.6 x 3.62 x 1.89 inches
  • Item Weight:4.3 ounces
  • Manufacturer:Gain Express Holdings Ltd


  • Display: double temperature and double salinity / 30 x 18 mm LCD dimensions for three units of measurement (ppm,%, s.g)
  • Measuring range: 0.950~9999ppm or 10.0ppt~100.0ppt or 0. 0% / 10. 0% or 0. 950 / 1. 080 (S.G.) Based on NaCl, ±% F.S ±1 bit / ±0.5 °C accuracy
  • Power / sensor: 4 LR44 button batteries
  • Features: waterproof IP65/ one-button calibration / automatic shutdown and non-sleep mode disable / multipoint calibration

#10 Instant Ocean Tk504 SeaTest Hydrometer

Instant Ocean Tk504 SeaTest Hydrometer Cover

When keeping clean, when you dump the first spoonful of water and slowly let it in so that there are no bubbles on the weighing meter, and when the water temperature is at 70 ℃, the reading is very accurate. I recently purchased a temperature compensated refractometer from a bulk coral reef supply along with a calibration fluid. I compared the reading with this hygrometer and the calibrated refractometer. The readings are the same.

  • Description:Instant Ocean Aquarium Water Test Hydrometer, Marine Salt & Gravity Lavel Testing Scale
  • Brand:Instant Ocean
  • Product Dimensions:6.3 x 4.2 x 1.3 inches ; 1.6 ounces


  • Accurate: accurate full range reading-accurate to + /-0
  • Ocean hydrometer: test the salinity and specific gravity of the marine aquarium to help maintain a healthy tank
  • Super wide stabilizer base: two-color scale, with safety zone, simple effect
  • Ready to use: just dip the water into the aquarium and put it on the horizontal plane to read.
  • Easy to read: clearly marked to display the results

Product Compare

# TOP 1-Refractometer Fish... 2-Exo Terra PT2466 H... 3-Coralife Energy Sa... 4-RZ Refractometer P... 5-AUTOUTLET Refracto... 6-SunGrow Salinity A... 7-GXSTWU Hygrometer... 8-Aquarium Salinity... 9-Salinity 100 0ppt... 10-Instant Ocean Tk50...
Product Refractometer Fishkeeping Automatic Temperature Compensation Thumbnail Exo Terra PT2466 Hygrometer Thumbnail Coralife Energy Savers ACLAF877 Hydrometer Thumbnail RZ Refractometer Professional Monitoring 1 000 1 070 Thumbnail AUTOUTLET Refractometer Thumbnail SunGrow Salinity Aquarium Refractometer Remarkable Thumbnail GXSTWU Hygrometer Thermometer Temperature Terrariums Thumbnail Aquarium Salinity Refractometer Saltwater Tank Dual Thumbnail Salinity 100 0ppt 0 95 1 08 Measurement Saltwater Thumbnail Instant Ocean Tk504 SeaTest Hydrometer Thumbnail
Customer Reviews
Product Dimensions 2 x 3 x 8 inches ; 8.8 ounces 0.5 x 4.1 x 7 inches 6.7 x 0.8 x 4.7 inches ; 3.2 ounces - 7.9 x 3.5 x 2.4 inches ; 8.5 ounces - 2.1 x 0.7 x 1.3 inches ; 0.96 ounces 7 x 1.5 x 1.5 inches ; 3.68 ounces - 6.3 x 4.2 x 1.3 inches ; 1.6 ounces
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