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Red Sea Seawater Refractometer

4.5 4.5 out of 5 stars 127 ratings
$74.99
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Purchase options and add-ons

  • Directly reads the absolute salinity of seawater at 25°c/77 0f ( no need for seawater or temperature compensation factors)
  • Specifically designed for the ionic content of seawater (NSW)
  • Calibrated for seawater (NSW) at 25oc/77of (most standard refractometers are calibrated at 15oc/59of )

Customer ratings by feature

Easy to use
3.6 3.6
Accuracy
3.6 3.6
Value for money
3.3 3.3
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Red Sea Seawater Refractometer
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AccuBrate Refractometer and Hydrometer Salinity Calibration Fluid – Solution to Accurately Calibrate Refractometer and Hydrom
$10.99 ($5.44/Fl Oz)
Get it as soon as Thursday, May 9
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Product details

  • Is Discontinued By Manufacturer ‏ : ‎ No
  • Product Dimensions ‏ : ‎ 3 x 3 x 8 inches; 11.2 ounces
  • Item model number ‏ : ‎ RS7945
  • Date First Available ‏ : ‎ July 2, 2014
  • Manufacturer ‏ : ‎ Red Sea
  • ASIN ‏ : ‎ B00LGUP210
  • Customer Reviews:
    4.5 4.5 out of 5 stars 127 ratings

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Red Sea Seawater Refractometer

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Product Description

Red Sea’s Seawater Refractometer offers exceptional accuracy, for measuring the absolute salinity of seawater at a temperature of 25oC/77 0F. Most refractometers used within the aquarium hobby are not specifically designed for reef aquariums and use an algorithm for the measurement of brine (NaCl – rather than seawater) and at a temperature of 15oC/59 0F rather than 25oC/77 0F. Thus, a measurement deviation of up to 1.5ppt is possible, which can have a significant adverse effect on coral growth and coloration.

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use as directed

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Price$74.99$59.95$15.99$23.99-29% $35.98
List: $50.48		$7.20
Delivery
Get it May 8 - 13
Get it May 9 - 14
Get it as soon as Thursday, May 9
Get it as soon as Thursday, May 9
Get it as soon as Thursday, May 9
Get it as soon as Monday, May 13
Customer Ratings
4.54.5 out of 5 stars127
3.83.8 out of 5 stars18
4.54.5 out of 5 stars422
4.54.5 out of 5 stars35
4.64.6 out of 5 stars4,230
4.54.5 out of 5 stars364
Easy to use
3.6
—
4.5
—
4.4
4.0
Accuracy
3.6
—
4.4
—
4.1
3.7
Sold By
Deal4K
Plants N Fins
Hallocool
Garden Boss
Amazon.com
Amazon.com

Customer reviews

4.5 out of 5 stars
4.5 out of 5
127 global ratings

Customers say

Customers like the quality and ease of use of the pet supplies. For example, they mention it's a good brand, and easy to use. That said, opinions are mixed on accuracy and value.

AI-generated from the text of customer reviews

16 customers mention16 positive0 negative

Customers are satisfied with the quality of the pet supplies. They mention that it's a good product for a reasonable price. Some say that the overall build quality and case are good. Overall, most are happy with the value of the product.

"Works great, expensive, easy to use, good quality." Read more

"...Its super easy to use and the peace of mind is priceless. I was running on luck before I bought this. great product." Read more

"...They are around 30 and they are super solid and accurate...." Read more

"...The overall build quality and case is good, unfortunitly its performance is not on par." Read more

12 customers mention12 positive0 negative

Customers find the pet supplies easy to use. They mention it's super easy, accurate, fast, and easy to read. They also say it'll mix saltwater to exactly 1.025 SG.

"Works great, expensive, easy to use, good quality." Read more

"...This particular refractometer is awesome. Its super easy to use and the peace of mind is priceless. I was running on luck before I bought this...." Read more

"This refractometer is really easy to use and because it's from Red Sea, I know it's a great product...." Read more

"...I mix my own saltwater, and it is easy to mix to exactly 1.025SG -- you can see the difference between 1.024, 1.025, 1.026..." Read more

26 customers mention12 positive14 negative

Customers are mixed about the accuracy of the refractometer. Some mention it's very accurate, precise, and easy to use, while others say that it didn't hold calibration.

"...Second issue is the refractometer will not hold calibration for more then a day. Its a bit odd why that is...." Read more

"...It's accurate, and easy to calibrate. I love it!" Read more

"...Like many of the other reviewers have stated, this unit does not hold calibration from one day to the next...." Read more

"...This particular refractometer is awesome. Its super easy to use and the peace of mind is priceless. I was running on luck before I bought this...." Read more

14 customers mention9 positive5 negative

Customers are mixed about the value of the pet supplies. Some mention it works great and is perfect, while others say it's worthless and not worth the money.

"Once you learn how to use this piece of equipment properly, it is perfect. It's accurate, and easy to calibrate. I love it!" Read more

"...to get a better visual scale resolution which is nice and it works albeit a pain which could cause new users to the device to get false readings..." Read more

"Works great, expensive, easy to use, good quality." Read more

"Works great. Always had a glass hydrometer which leaves a little +/- variance due to the water on glass. This thing is great!" Read more

Major Flaws - Will not hold calibration
2 Stars
Major Flaws - Will not hold calibration
Red Sea Refractometer will be on my DO NOT buy list.I have purchased 2 of these Refractometer to verify the claims.First issue with the unit is the PPT and SG "0" do not line up. See attached pictures. Using RO/DI water I calibrated the unit to use the PPT scale. In this setting the SG will be in the negatives. I have called Red Sea regarding this, and they stated it was normal.Second issue is the refractometer will not hold calibration for more then a day. Its a bit odd why that is. I will calibrate the unit using RO/DI to 0 but the next day it will be off 0 again, making me calibrate the unit once more. Both of my Red Sea Refractometer does this. Even after calibration the 2 units sometimes will not give the same results. Same water, same temp, same location, but the readings will be off from each other. So that prompted me to use a calibration fluid at 35ppt at 25C. since this refactometer is ratied at that temperature. Once I have done that I will used RO/DI water to see if it levels will read 0, and it will not be 0 Both meters will be off. One refractometer will be negative values while the other will be positive. On its good day it will read 0.I have a cheap refractometer I purchased a while back that still holds calibration. When I calibrate that unit it will read 35ppt with fuild and 0 with RODI without any adjustments.In conclustion, if you want to be constantly calibrating your refractrometer then this unit is for you.The overall build quality and case is good, unfortunitly its performance is not on par.
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Top reviews from the United States

Sherri Meyer
5.0 out of 5 stars Excellent tool!
Reviewed in the United States on April 17, 2023
Verified Purchase
Once you learn how to use this piece of equipment properly, it is perfect. It's accurate, and easy to calibrate. I love it!
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Master Technician
5.0 out of 5 stars Works great
Reviewed in the United States on September 9, 2021
Verified Purchase
Works great, expensive, easy to use, good quality.
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Miguel M.
5.0 out of 5 stars This particular refractometer is awesome. Its super easy to use and the peace ...
Reviewed in the United States on July 13, 2016
Verified Purchase
Do not skimp out on buying this!!! This is mandatory equipment for every reefer period. This particular refractometer is awesome. Its super easy to use and the peace of mind is priceless. I was running on luck before I bought this. great product.
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Phil Demarest
5.0 out of 5 stars Quality Item!
Reviewed in the United States on October 13, 2015
Verified Purchase
This refractometer is really easy to use and because it's from Red Sea, I know it's a great product. I had to initially calibrate it and it's held it's calibration for a while now. I like the fact that it is made specifically for saltwater, and not for brine water. I highly recommend this for the serious saltwater hobbyist.
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J. Bobgan
5.0 out of 5 stars Excellent!
Reviewed in the United States on April 25, 2015
Verified Purchase
Best refractometer I've found for saltwater/reef aquarium use. Scale reads between 1.000-1.030SG and 0-40PPT. With the expanded scale (compared to many other refractometers), it is fairly easy to read to 0.001SG. I mix my own saltwater, and it is easy to mix to exactly 1.025SG -- you can see the difference between 1.024, 1.025, 1.026...
3 people found this helpful
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Dave
5.0 out of 5 stars Awesome tool, a must have for a reef tank
Reviewed in the United States on October 14, 2019
Verified Purchase
Works great. Always had a glass hydrometer which leaves a little +/- variance due to the water on glass. This thing is great!
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Joshua Updyke
4.0 out of 5 stars Four Stars
Reviewed in the United States on September 8, 2017
Verified Purchase
Works great.
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D98837
1.0 out of 5 stars DO NOT BUY. Will not hold calibration, even for a few minutes.
Reviewed in the United States on December 1, 2016
Verified Purchase
The Red Sea Seawater Refractometer will not maintain calibration.

Example: Today I calibrated the device and got a reading of .035 on a water sample. But experience has taught me not to trust this refractometer with my reef tank, so I did another measurement of the same water sample, in the same room, at the same room temperature 5 minutes later and got a reading of .025. This happens roughly 80% of the time. I usually take 5 or 6 readings and average out the results in an attempt to improve the accuracy.

I contacted Red Sea customer support via email, described the situation (goes out of calibration within a few minutes) and got this reply "Unfortunately yes, this normal for our refractometer. Anything from a temperature change to vibrations can offset the calibration." And that is the entirety of her response. Remember, we're talking within a few minutes that the device goes out of calibration.

But as hard to swallow as her response might be, it still skirts the issue by adding a temperature/vibration caveat. So I clarified my question: "Without temperature fluctuations and without vibration is it normal behavior for the Red Sea Refractometer to need calibration every 5 to 10 minutes during use?" and did not get another response from them.

So when considering a purchase listen to the opinion of Red Sea customer support: This is normal behavior. And in my opinion, that makes the Red Sea Refractometer unusable.

Update 1-25-17: I purchased a Milwaukee Digital Refractometer MA887 and can't believe how easy and accurate it is. Turns out that my tank salinity was way off thanks to the Red Sea device. Now I understand why my seahorses and corals were dying even though my water parameters were perfect. Do yourself a favor and get the Milwaukee Digital Refractometer. It's accurate, easy and gives you a reliable reading with the push of a button.

 Milwaukee Instruments MA887-BOX Digital Refractometer for Seawater Measurements with Protective Padded Hardshell
5 people found this helpful
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Top reviews from other countries

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Shelley Tkachyk
5.0 out of 5 stars Best i have bought, easy to use
Reviewed in Canada on July 1, 2020
Verified Purchase
I was not too sure what to expect after purchasing due to mixed reviews. I am impressed. This is really to use, you don't need calibration solution just use your RO water to calibrate to 0. I check every time i use it and after about 6 uses i had to slightly calibrate but not significantly. I have used the fluval salinity meter and had to replace yearly so i thought i would try a refractometer and i would never go back. Calibration takes seconds and at least you do not need to take about 10 -15 min like the digital ones getting it perfect. I have a digital one too and hate it, too much time spent calibrating and too much money on calibration solution. This one is perfect and simple to use, it has a nice case, instruction book is easy to follow, calibration tool and a plastic dropper. all fit in case nicely.
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Jovany lozano
5.0 out of 5 stars Todo exelente
Reviewed in Mexico on March 4, 2017
Verified Purchase
Exelente todo me llego bien tiempo y forma lo recomiendo al 100 pero el unico problema fue que me realizaron un csrgo dovle a mi tarjeta y aun no me responden de eso saludos
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Amazon Customer
5.0 out of 5 stars Perfect!
Reviewed in Canada on August 2, 2018
Verified Purchase
Great tool for salt water tanks, it’s nice and heavy and so much cheaper then the store.
I used a hydrometer and i will never go back to that, this is simple and fast, when i received it it was well calibrated and kept the calibration till now!
I recommend this red sea refractometer this company has very good products.
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Steven B.
5.0 out of 5 stars Great quality product
Reviewed in Canada on April 7, 2015
Verified Purchase
Great quality product !!!!
I love Red Sea, they always have very innovative products, and of high quality at that.
I love this refractometer, it is accurate, i realised that my old hydrometer (Instant Ocean, had a noticeable difference of reading.)
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Elaine
5.0 out of 5 stars Five Stars
Reviewed in Canada on May 21, 2016
Verified Purchase
its great and very easy to use
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