Instant Ocean Testing Hydrometer for Aquariums, 1 count

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About This Item

Details

  • 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

Instructions

Learn More About Instant Ocean From Our Team of Experts

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Questions & Answers

3 Customer Questions

what the selenium level be for brackish water

Answer by Chewy • Dec 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 Chewy • Apr 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 Chewy • Jan 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.
Reviews
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4.0
Rated 4 out of 5 stars
36 Ratings
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17 Customer Reviews

Rated 1 out of 5 stars
By Kim on Oct 26, 2025

Very inaccurate Not usable

Unfortunately I tried two of these and both were extremely off with this company. It was showing salt in my tap water, it was so off. When I tested my current main

Unfortunately I tried two of these and both were extremely off with this company. It was showing salt in my tap water, it was so off. When I tested my current main tank, they both floated straight up, as if it was so high in salinity that it was off the charts. Thankfully, I have another one and the water was actually perfect at 1.023. Not off the charts as this Instant Ocean hydrometer was showing. Both are in the trash :-(

Rated 3 out of 5 stars
By Jen on Dec 14, 2025

good enough for what it is

I think the digital kind may be easier to use, and this one fills oddly, but it does its job

I think the digital kind may be easier to use, and this one fills oddly, but it does its job

Rated 5 out of 5 stars
By Matthew on Nov 22, 2025

Price

Easy to use if used properly

Easy to use if used properly

Rated 5 out of 5 stars
By Ferg on Jan 8, 2025

Simple testing

Hydrometer has multiple scale readings so I can keep the tank balanced

Hydrometer has multiple scale readings so I can keep the tank balanced

Rated 1 out of 5 stars
By Roy on Apr 2, 2024

Wildly Inaccurate

Wow, what a waste of my money, time and effort. This Hydrometers calibration is way off, it reads differently each time it's used to test the salinity of my marine

Wow, what a waste of my money, time and effort. This Hydrometers calibration is way off, it reads differently each time it's used to test the salinity of my marine FOWLR tank. I took it to a LFS local fish store and they tested it and got the same results. Each time the tech used it she got a different reading. I filled it with saltwater and let it sit overnight per the instructions. I had to purchase a replacement at the LFS in order to complete my water change. Such a pain! Tanks, Tanks alot Chewy...

Rated 1 out of 5 stars
By Thomas on Dec 9, 2024

Instant ocean hydrometer

Did not work correctly

Did not work correctly

Rated 5 out of 5 stars
By Nicole on Sep 24, 2023

Unreliable

Gave different results each time I used it. Save yourself the headache and spend a few extra dollars and get a refractometer instead - reliable and easy to use.

Gave different results each time I used it. Save yourself the headache and spend a few extra dollars and get a refractometer instead - reliable and easy to use.

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

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

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.

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