Editor's Choice - Our Favorite Instant Ocean Aquarium Hydrometers

1. Instant Ocean SeaTest Hydrometer

User Ratings: 59 6

Instant Ocean TK-504 First Impressions

"Calibrate it, use it."

Make your own by simply boiling some water and collecting the condensate. This one here was much cheaper,& exactly the same as they sold in the store. My only criticism would be that it's a little too dark. Normally that gives the more accurate reading. Used distilled water to calibrate, the screw is located under the rubber cap. Once I adjusted the refractometer, my aquarium salinity read 1. Hate the batteries, but once loaded, it seems to work fine.

  • Instant Ocean SeaTest Hydrometer
  • Marine hydrometer: Tests salinity and specific gravity in marine aquariums to help maintain a healthy tank
  • Accurate: Precise, full-range readings - accurate to +/- 0
  • Ready to use: Simply dunk in aquarium to fill with water, then set on level surface to read
  • Easy to read: Clearly marked to show results
  • Extra-wide stabilizer base: Two-color scale with a safe zone for simple results
  • Manufacture: Instant Ocean
  • Item Weight: 0.8 ounces
  • Product Dimensions: 6.3 x 4.2 x 1.3 inches
  • Editor's Impressions Of The Instant Ocean TK-504
  • Accuracy
  • Quality
  • Value For Money
  • Affordability

Instant Ocean TK-504 Final Thoughts

"Good price."

Simple to use, but if there are any air bubbles the results will be way off. The instant ocean hydrometer will always be right. 026 with the new Aquatic Experts fluid. Now its easy to make sure I have the correct amount of salt in my aquariums. Looks to provide very accurate readings. Easy to use, easy to clean, easy to read. My only criticism would be that it's a little too dark.

Overall Score
4.2


(426 Points)

2. Instant Ocean SeaTest Hydrometer

User Ratings: 59 6

Instant Ocean TK-504 First Impressions

"Calibrate it, use it."

Make your own by simply boiling some water and collecting the condensate. This one here was much cheaper,& exactly the same as they sold in the store. My only criticism would be that it's a little too dark. Normally that gives the more accurate reading. Used distilled water to calibrate, the screw is located under the rubber cap. Once I adjusted the refractometer, my aquarium salinity read 1. Hate the batteries, but once loaded, it seems to work fine.

  • Instant Ocean SeaTest Hydrometer
  • Marine hydrometer: Tests salinity and specific gravity in marine aquariums to help maintain a healthy tank
  • Accurate: Precise, full-range readings - accurate to +/- 0
  • Ready to use: Simply dunk in aquarium to fill with water, then set on level surface to read
  • Easy to read: Clearly marked to show results
  • Extra-wide stabilizer base: Two-color scale with a safe zone for simple results
  • Manufacture: Instant Ocean
  • Item Weight: 0.8 ounces
  • Product Dimensions: 6.3 x 4.2 x 1.3 inches
  • Editor's Impressions Of The Instant Ocean TK-504
  • Accuracy
  • Quality
  • Value For Money
  • Affordability

Instant Ocean TK-504 Final Thoughts

"Good price."

Simple to use, but if there are any air bubbles the results will be way off. The instant ocean hydrometer will always be right. 026 with the new Aquatic Experts fluid. Now its easy to make sure I have the correct amount of salt in my aquariums. Looks to provide very accurate readings. Easy to use, easy to clean, easy to read. My only criticism would be that it's a little too dark.

Overall Score
4.2


(426 Points)

3. Pen Type Salinity & Temp Meter Measurement Units Checker Quality Tester ATC for Pond Pool Saltwater ...

User Ratings: 36 25

TEKCOPLUS SMTK-49_SOL First Impressions

"So here's the verdict."

Just give me one simple, accurate reading to go by, and I'm happy. This is perfect to keep a check on the salt level in your tank. He is too cute not to want to take care of properly. Bought this as a back up refractometer. Get precise salinity readings in moments. The unit is really easy to calibrate and used. My only criticism would be that it's a little too dark.

  • Pen Type Salinity & Temp Meter Measurement Units Checker Quality Tester ATC for Pond Pool Saltwater Aquarium Cooking Seawater Drinking Water (Salinity Meter 70.0ppt + Buffer Sol'n)
  • Ideal for checking salt in fish tanks and aquariums, water monitoring, seawater-prepared food solutions, holding tanks and more!
  • Measuring Range: Salinity: 0.00~10.0 ppt (NaCL) and 10.1~70.0ppt (NaCL)
  • Auto Power-Off Function with disable feature
  • °C/°F unit switchable ,Easy one-touch calibration, Waterproof Rating: IP65
  • Calibration set: Buffer NaCI 50ppt and calibration guideline
  • Manufacture: TekcoPlus Ltd
  • Editor's Impressions Of The TEKCOPLUS SMTK-49_SOL
  • Accuracy
  • Quality
  • Value For Money
  • Affordability

TEKCOPLUS SMTK-49_SOL Final Thoughts

"Measurement does work."

I have to recalibrate it ever use though which worries me sometimes. Just rinse with warm water afterwards. I bought this salinity meter for my aquarium. I bought this and a hydrometer because of the reviews saying its not accurate. I have gone two years in this hobby with a hydrometer. Easy to use, easy to clean, easy to read. Compare it with the refractometer and adjust the refractometer so that it matches.

Overall Score
3.6


(5 Points)

4. AUTOUTLET Refractometer Saltwater Aquarium for Seawater,Pool,Tank,Testing,Marine Fishkeeping, 0-100P...

User Ratings: 83 2

AUTOUTLET 8541957195 First Impressions

"These seem spot on."

Not sure how accurate it is, but it's a good reference point. Ambient room light at night is not enough and makes what you're viewing dark. If you read the directions in the box for the refractometer it's for freshwater. And it is much more accurate than my old salinity meter. Waterproof if you accidentally drop it in the pool. My corals will be much happier now. It is a little cheaper made but it works great for the cost!

  • AUTOUTLET Refractometer Saltwater Aquarium for Seawater,Pool,Tank,Testing,Marine Fishkeeping, 0-100PPT & 1.000-1.070 Salinity Tester with ATC Function Hydrometer Specific Gravity Salinity Meter Kit
  • 【Salinity Refractometer】Measure Salt Water or Salinity of Water,Monitor and Control the Concentration of Salt Water and Brine,Ideal for Aquariums and Marine Applications.
  • 【Measures on 2 Scales】Specific Gravity (D 20/20) and parts per thousand and replaces your poor quality and difficult to read hydrometer.
  • 【Density Measurement Range】1.0-1.070, Minimum Scale is 0.001.
  • 【Concentration Measurement Range】0-100‰, Minimum Scale is 1‰.
  • 【ATC】Automatic Temperature Compensation, 0-10°C.
  • Due to the difference of human focal lengths,when during adjusting, you may just need to rotate in reverse or re-adjust the distance between your eye and the eyepiece.
  • It's necessary to keep the surrounding environment with sufficient brightness and suitable temperature during use. Generally,there is no error in the temperature between 10℃-30℃.(50℉-86℉)
  • Specific Gravity (D 20/20) and parts per thousand and replaces your poor quality and difficult to read hydrometer.
  • Manufacture: AUTOUTLET
  • Product Dimensions: 7.87 x 3.54 x 2.36 inches; 8.48 Ounces
  • Editor's Impressions Of The AUTOUTLET 8541957195
  • Accuracy
  • Quality
  • Value For Money
  • Affordability

AUTOUTLET 8541957195 Final Thoughts

"2 failed, 3 did not."

Just rinse with warm water afterwards. I bought this and a hydrometer because of the reviews saying its not accurate. Now that it's calibrated I love it! I HIGHLY recommend this to Aquarists! I have purchased before will buy again! I got this to have a more accurate read than the hydrometer. Too that makes it appear too cheap.

Overall Score
4.7


(757 Points)

5. Pen Type Salinity & Temperature Meter ATC NaCl Salt Water Quality Tester for Saltwater Aquarium Hydr...

User Ratings: 49 17

Gain Express 837-2 First Impressions

"Easy to calibrate."

Just rinse with warm water afterwards. I run brackish tanks and it works perfectly. Hate the batteries, but once loaded, it seems to work fine. I tried it over and over and no bubbles! Excellent piece of equipment for the price. The water was at what I expected it should be. 026 and the tank isn't, new animals will go into shock.

  • Pen Type Salinity & Temperature Meter ATC NaCl Salt Water Quality Tester for Saltwater Aquarium Hydroponics Food
  • MEASURING RANGE: 0~9999 ppm or 10.0ppt~100.0ppt or 0.0%~10.0% or 0.950~1.080 (S.G.) based on NaCl with ±%F.S ±1 digit / ±0.5°C Accuracy
  • DISPLAY: Dual Temperature and Salinity in four measurement units (ppm, ppt, %, S.G) / 30 x 18mm LCD Size
  • APPLICATION: Salinity measurement in fish pond, tank, aquariums, laboratories, food processing, hydroponics, Aquaculture, and other water monitoring facilities.
  • FEATURES: Waterproof IP65 / One touch calibration / Auto power off and Non-Sleep mode disable / Multi points calibration
  • POWER SUPPLY / SENSOR : 4 x LR44 button batteries
  • User friendly easy to operate with One-touch calibration
  • Manufacture: Gain Express Holdings Ltd
  • Batteries: 4 LR44 batteries required.
  • Editor's Impressions Of The Gain Express 837-2
  • Accuracy
  • Quality
  • Value For Money
  • Affordability

Gain Express 837-2 Final Thoughts

"So, it does seem to work."

But with alittle persistance I am able to read it. Perfrct for someone learning or anyone for that matter. Once I adjusted the refractometer, my aquarium salinity read 1. Works great,& comes in a storage box. Works well on my Saltwater Aquarium. It did not need adjusting to calibrate, though I tried to just to see how it worked. Would be nice if stem were slightly larger for easier read.

Overall Score
3.8


(99 Points)

6. RZ Aquariums Salinity Refractometer for Seawater Marine Fish-Keeping, Dual Scales Specific Gravity S...

User Ratings: 74 3

RZ First Impressions

"Great product."

I bought this salinity meter for my aquarium. I needed this product and it is a lot less expensive than the local aquarium store. When I saw the price offered on this one, I decided to buy and I love it. Works well on my Saltwater Aquarium. I was surprise that the product was really cheap compare to the other ones. But there are some ways to keep on getting accurate readings. Too that makes it appear too cheap.

  • RZ Aquariums Salinity Refractometer for Seawater Marine Fish-Keeping, Dual Scales Specific Gravity Salinity Meter Hydrometer 0-100ppt & 1.000-1.070, Saltwater Tester with ATC Function
  • Measures on 2 Scales: Aquariums refractometer features Specific Gravity (D 20/20) 1.000-1.070sg and parts per thousand 0-100PPT (1‰=1ppt=1000ppm)
  • Seawater refractometer measures saltwater or salinity of water, ideal for aquarium, marine monitoring, fish-keeping,salty pools&spas and etc.
  • ATC Function: salty water refractometer with automatic temperature compensation, allow you obtain accurate readings easier and faster
  • Salinity Refractometer is made of aluminum body and ABS rubber light and very sturdy, comes with a hard plastic case, a mini screwdriver, a dropper
  • Easy to Use: put 2-3 drops on the saltwater’s prism, towards light then to get the accurate readings through the optic eyepiece, ideal for replacement the poor quality and difficult to read hydrometer refractometer
  • Manufacture: RZ
  • Editor's Impressions Of The RZ
  • Accuracy
  • Quality
  • Value For Money
  • Affordability

RZ Final Thoughts

"Seems to work fine."

I will get one later but for now this will do, since im just starting. Comes with a nice carrying case for easy and secure transportation. I decided to upgrade and it was easy to calibrate. Plenty of info on YouTube and the web if you don't know how. Small problem with bubbles on the needle but other than that no issues. The reading is big enough for you to read and it comes with the batteries. Be sure to adjust the focus by turning the eye focal when you first receive.

Overall Score
4.6


(296 Points)

7. GXSTWU Reptile Hygrometer Thermometer LCD Display Digital Reptile Tank Hygrometer Thermometer with H...

User Ratings: 71 5

GXSTWU HY-2 First Impressions

"Couldn't be happier."

I compared the readings using this hygrometer and the calibrated refractometer. But with alittle persistance I am able to read it. Not sure how accurate it is, but it's a good reference point. There are conversion charts and tables online. I will get one later but for now this will do, since im just starting. So once your instant ocean shows a measurement. Find a good light source to make reading easier.

  • GXSTWU Reptile Hygrometer Thermometer LCD Display Digital Reptile Tank Hygrometer Thermometer with Hook Temperature Humidity Meter Gauge for Reptile Tanks, Terrariums, Vivarium
  • 100% Brand New and High-Quality Reptile Tank Thermometer Hygrometer: Precise supervision of the temperature and air humidity in terrariums, vivariums and reptile tanks.
  • Stylish Design: Stylish looking digital vivarum thermometer with hook and loop for easy to install to any reptile tanks or terrariums. Comes with a battery so you can use the thermometer immediately.
  • Fantastic Value: This accurate reptile thermometer and hygrometer allows you to monitor the temperature and humidity in the reptile tanks at all times to makesure your beloved reptiles are in perfect health.
  • Fahrenheit Celsius Convertible: Temperature can be display in Fahrenheit or Celsius by press the C/F hole on the back of the item with a paper clip.
  • Quality Guaranteed: Our carefully sourced range of thermometer hygrometers are manufactured to the highest of standards our customers expect. And provide 365 days warranty, in case of any quality problems, please feel free to contact us by email, we will give you a satisfactory solution.
  • Manufacture: Cangda Electronics Co., Ltd.
  • Product Dimensions: 2.09 x 0.67 x 1.3 inches; 0.92 Ounces
  • Batteries: 1 LR44 batteries required. (included)
  • Editor's Impressions Of The GXSTWU HY-2
  • Accuracy
  • Quality
  • Value For Money
  • Affordability

GXSTWU HY-2 Final Thoughts

"Seems pretty solid."

Hate the batteries, but once loaded, it seems to work fine. If you let it sit in the tank overnight, it definitely gives an accurate reading. Like that it comes with everything needed. Get precise salinity readings in moments. I have to recalibrate it ever use though which worries me sometimes. This one read perfect, and the others were completely inaccurate. Plus it is super easy to use and clean.

Overall Score
4.4


(265 Points)

8. ZRM&E Seawater Hydrometer for Aquarium Aquaculture Seawater Densimeter Ocean Hydrometer Salinity Met...

User Ratings: 70 30

ZRM&E First Impressions

"Gave me confidence."

YOU WILL NOT get an accurate reading if there are bubbles on the needle. I have purchased before will buy again! I felt it wasn't accurate which was verified by my LFS. Very quick to calibrate and to use. It says in the instructions to use distilled water. I bought this refractometer as a more accurate option for salinity than a hydrometer. Don't spend your money on calibration solution.

  • ZRM&E Seawater Hydrometer for Aquarium Aquaculture Seawater Densimeter Ocean Hydrometer Salinity Meter for Fish Tank Salinity Specific Gravity Test
  • Made of high quality plastic, aquarium transparent, automatic accurate reading brine hydrometer
  • Accurate, durable and easy to read salt and specific gravity of your marine aquarium, small and waterproof. If the specific gravity is between 1.000-1.019, it indicates that the specific gravity is low; if the specific gravity is between 1.020-1.023, it indicates that the specific gravity is normal; if the specific gravity is between 1.024-1.030, it indicates that the specific gravity is high
  • The external range of the scale indicates salinity (PPT), and the internal range of the scale indicates gravity. And clearly mark the safe area. Application range: 0-40 degrees (1.000-1.030). If the salinity PPT is between 32-40, it indicates that the salinity is high; if the salinity PPT is between 27-31, it indicates that the salinity is normal; if the salinity PPT is between 0-26, it indicates that the salinity hydrometer is low
  • Wide range of applications: Suitable for salt water and sea water fish tanks. Perfect for testing salinity and specific gravity of saltwater and seawater tanks, including solubility and specific gravity scales. Suitable for fresh water and sea water
  • Easy to read swing arm pointer and ultra wide stable base can provide accurate test results
  • Manufacture: DGHP
  • Editor's Impressions Of The ZRM&E
  • Accuracy
  • Quality
  • Value For Money
  • Affordability

ZRM&E Final Thoughts

"Great Product, Thanks!"

YOU WILL NOT get an accurate reading if there are bubbles on the needle. Get precise salinity readings in moments. If you let it sit in the tank overnight, it definitely gives an accurate reading. Compare it with the refractometer and adjust the refractometer so that it matches. Don't care much for having to post a review in order to activate warranty. Even the smallest bubble will throw the measurements way, way off. I would recommend this product to anyone that has a marine aquarium.

Overall Score
3.8


(4 Points)

9. LemonBest 0%-10% Automatic Temperature Compensation Salinity Refractometer Salt Water Aquariu...

User Ratings: 75 5

LemonBest First Impressions

"Great tool."

I don't want to deal with temperature correction or. When I compared it to what my local pet store was reading my water at it was dead on. Used distilled water to calibrate, the screw is located under the rubber cap. This one here was much cheaper,& exactly the same as they sold in the store. At first, I was getting bubbles sticking to the rotating arrow. Definitely a lot cheaper than a refractometer. I decided to upgrade and it was easy to calibrate.

  • LemonBest 0%-10% Automatic Temperature Compensation Salinity Refractometer Salt Water Aquarium by Lemonbest
  • Features with automatic temperature compensation (ATC) function
  • Designed for testing the concentration of salt water and brine, ideal for aquariums, marine monitoring and quality control in research and clinical laboratories
  • With just a couple of drops of aquarium water you know exactly what the salinity is
  • Measures on 2 scales, specific Gravity (D 20/20) and parts per thousand (‰), provides a direct reading of the specific gravity and concentration of salt in water
  • Comes with a hard case, dropper, screwdriver and cleaning cloth
  • Manufacture: Lemonbest
  • Product Dimensions: 7.87 x 1.57 x 1.57 inches; 3.88 Ounces
  • Editor's Impressions Of The LemonBest
  • Accuracy
  • Quality
  • Value For Money
  • Affordability

LemonBest Final Thoughts

"Easy to use."

Make sure to knock out the bubbles on the white dial by hitting it with your knuckle. It works OK but seems pretty flimsy and it's feel that way. My only criticism would be that it's a little too dark. I don't know if that's a positive or negative but just different. Just rinse with warm water afterwards. I bought this and a hydrometer because of the reviews saying its not accurate. Pretty darn accurate for the price.

Overall Score
4.5


(315 Points)

10. Coralife BioCube Mini Aquarium Hydrometer

User Ratings: 37 28

Coralife 100115642 First Impressions

"NO BUBBLES!"

My corals will be much happier now. Every time I leave to do something I come back and it's at the bottom of my tank. And it is much more accurate than my old salinity meter. This device is a godsend and so much easier and cleaner to use. It is a little cheaper made but it works great for the cost! Just give me one simple, accurate reading to go by, and I'm happy. When I saw the price offered on this one, I decided to buy and I love it.

  • Coralife BioCube Mini Aquarium Hydrometer
  • Can remain submerged inside your aquarium or sump
  • Know your salinity in a glance
  • Compact design allows for discreet placement in the aquarium
  • Ideal for all saltwater aquariums and sumps
  • Manufacture: Central Garden & Pet
  • Product Dimensions: 3.9 x 1 x 6 inches; 0.8 Ounces
  • Editor's Impressions Of The Coralife 100115642
  • Accuracy
  • Quality
  • Value For Money
  • Affordability

Coralife 100115642 Final Thoughts

"I say it works very well."

Waterproof if you accidentally drop it in the pool. Do not spend money on calibration fluid to calibrate this meter. I use this for my 10g brackish and it works ok. I use this for my 10g brackish and it works ok. There are conversion charts and tables online. Wipe down glass surface to dry it and put it back on the shelf til next time. I would recommend you to purchase this and skip the other ones.

Overall Score
3.3


(57 Points)

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