Instant Ocean Testing Hydrometer for Aquariums, 1 count

By Instant Ocean
Rated 3.4 out of 5 stars
$11.84Chewy Price
$11.99Chewy Price
$11.25Autoship Price
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About This Item


  • Helps you reach correct salt level with a clear marked safe zone
  • Makes the difficult task of reaching the correct salt level in your marine aquarium much easier to use and read
  • Maintains the right level is vital to creating and maintaining a thriving marine environment
  • Reliable tool that provides full-range salinity and specific gravity readings, and it’s accurate to ± 0.001
  • Hands stay dry when filling while testing aquarium salt level and specific gravity

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Learn More About Instant Ocean From Our Team of Experts

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Fish TypeMarine FishBetta, Bottom Feeder, Cichlid...Betta, Cichlid, Goldfish, Marine Fish, Tropical FreshwaterMarine Fish, Marine InvertebrateBetta, Bottom Feeder, Cichlid...
Aquarium TypeSaltwaterSaltwater, FreshwaterSaltwater, FreshwaterSaltwaterSaltwater, Freshwater

Questions & Answers

3 Customer Questions

what the selenium level be for brackish water
Answer by ChewyDec 15, 2019
The world’s marine waters have a salinity between 32 and 35 parts per thousand. Brackish water, by definition, must be lower than the lowest value of this range. Many freshwater aquarium species can withstand (or benefit from, according to some) a certain level of salinity in their tank water. Calculating the salinity of water is done by measuring specific gravity (SG) with a hydrometer, or alternatively, conductivity via a meter. Both of these methods are temperature dependent – readings vary with the warmth of the water. For practical purposes, brackish aquarium water should range between 1.002 to 1.022 SG at a temperature of 77 degrees Fahrenheit. Most brackish aquarium fish can tolerate this range. A 50/50 mix of fresh and marine water would provide a salinity of 1.012 SG – a happy medium for a general brackish aquarium.

How does this hydrometer take into account water temperature?
Answer by ChewyApr 02, 2018
The hydrometer doesn't take into account the water temperature. It will read the salinity and specific gravity accurately at temperatures between 68 and 85 degrees Fahrenheit.

What's the lowest reading on the hydrometer? Needing to use this to slowly increase salt to acclimate tank from freshwater to brackish Need low reading of .002 Will this work ? And if not Do you sell refractometers?
Answer by ChewyJan 09, 2018
The lowest reading is 0 - 1.000. The Hydrometer is normally used for saltwater tanks so it has higher level readings, depending on how high the brackish level is it may not work. At this time we don't carry refractometers.

ReviewsWrite a Review

Rated 3.4 out of 5 stars
10 Ratings
Would recommend to a friend

10 Customer Reviews

Rated 5 out of 5 stars
By Turtletary on May 18, 2022

Works as expected

Always a good idea to make at least 3 readings and go with average. Readings could change from different locations in the tank... regardless what type Hydrometer is used. Salinity testing 101.

Rated 5 out of 5 stars
By Michael66 on Aug 15, 2021

Reliable and inexpensive

Have been using this hydrometer for decades and has given me accurate readings. After a year I purchase a second one to verify the accuracy of the first one, and replace it if necessary. Again it’s very inexpensive to replace. Thank you so much Chewy for always having such great service and quality products.

Rated 5 out of 5 stars
By VAReefer on Aug 16, 2021

Tested for accuracy.

The hydrometer reading is accurate when new. Needs to be replaced though every now and then.

Rated 1 out of 5 stars
By MichelleMV on Mar 2, 2021

Not accurate

Got my replacement today since the original was cracked upon arrival (thank you Chewy, it’s appreciated) however soon after I realized this thing is extremely inaccurate. Tried getting a reading three separate times (and yes I thoroughly rinsed before each use) and all three time readings were widely different. Even tested it on my tap water. And was still reading salinity. Save your money and get a refractometer instead. Very disappointed.

Rated 5 out of 5 stars
By Doug on Apr 8, 2021

Fast and cheap

I was surprised how fast chewy performed, jst a matter of days not weeks

Rated 5 out of 5 stars
By bfg1 on Jan 30, 2021


This works great and I appreciated the ease of ordering and the speed of delivery

Rated 1 out of 5 stars
By 123missingproduct on Jul 31, 2020

Struggling corals

I ended up buying the hanna salinity reader after reading bad reviews from this product. Tested both of them next to each other and the hydrometer read lower 1.024 and my hanna read 1.026! Don't waste your money on this product or your corals and fish will struggle. I thought my salinity was great for my corals and now I see it's on the high side.

Rated 1 out of 5 stars
By birdy on May 15, 2020

not accurate

Cannot get close to the same reading twice in a row. Very disappointed. With having the Instant Ocean name, thought I was getting a quality product.

Rated 1 out of 5 stars
By Jhonny on Sep 21, 2018

Waste of money, realized after 3 uses

Not very accurate, best get a refractometer for 7 to 10 dollars more... I'd return this hydrometer if my daughter didnt already destroy the packing.

Rated 5 out of 5 stars
By Robin on Feb 19, 2017

Great product

We've had saltwater fish for years and instant ocean has the best products and affordable.