Updated 2024
There are three methods to test the salinity of your water:
1. Hydrometer
2. Refractometer
3. Probe
I must mention a fourth, but I don’t recommend the tasting method as it is not accurate!
The most precise and best value, in my opinion is the standard hand held refractometer. For under $40, you can measure your aquarium’s salinity for a lifetime. It rarely requires calibration, and with proper cleaning, it can last for years.
What do I personally use after 10 years in this hobby? A mix of three things. I use a glass high-precision hydrometer in my fifty gallon seawater reservoir. I use a refractometer for my weekly water testing. And I use the Hanna Salinity Tester sometimes, although not as frequently as of late because you have to calibrate it frequently so I don’t always trust it.
1. Tropic Marin High Precision Hydrometer
I love this hydrometer, and you will too… If you use it in the right situation. The thing about this hydrometer is it is made of glass and super fragile. I have three because I was making a BRS video of one, and it shipped to me broken, so they shipped me a couple more just to make sure. The really fragile part is the skinny stem. Here’s the video I made on this.
Okay, so it’s not my most viewed video, but it should be! I mean come on… look at that thumbnail I made! 🙂
So here’s the thing about this hydrometer. It’s super accurate, as long as the water your testing is 77 degrees farenheit and still. So that means while you could use it in a five gallon bucket to test your freshly made seawater, I think it makes way more sense in a permanent water change setup, either a 20-30 gallon Brute trash can or a 50 gallon tub.
I have a 50 gallon barrel in my living room that has fresh seawater always inside, and I just leave this hydrometer in place. And because I always heat said water to 77 degrees, it’s super easy to just lift the lid and double check the salinity before doing my water changes.
Could you use this as your primary means of measuring salinity? Of course! Would I recommend it? No.
2. Milwaukee Digital Seawater Refractometer
While this option may be a bit pricey, it is undoubtedly one of the most accurate choices available. All you need to do is calibrate it with a bottle of distilled water, and then simply use a pipette to add water into the tester, providing you with an immediate reading.
If you value precision and want the utmost accuracy, this product would be a solid recommendation. It’s user-friendly, easy to clean, and the digital read-out ensures you can confidently obtain the most accurate readings possible.
Operating on the same principle as a hand-held refractometer, it offers the advantage of being easier to read and has a low probability of user error!
I own one, but I never use it. Why? Just because it is faster for me to use my handheld refractometer. And why pay well over $100 when a much less expensive refractometer exists?
That being said, I have some friends who love this thing, and it’s all they use, so to each their own.
3. Hanna Instruments Waterproof Salinity & Temperature Tester
This use to be my go to tester. It boasts user-friendly features such as easy usage, simple cleaning, and straightforward calibration. Just a quick rinse with RO/DI water after each use, and you’re good to go.
However, there are a couple of drawbacks to consider. Firstly, it requires monthly calibration, which isn’t a major inconvenience, but you’ll need to purchase their calibration packets.
The most significant drawback is that this tester is specifically designed for testing freshly made saltwater, not tank water. While many still use it for aquarium testing, this limitation can affect its accuracy over time. After a month of use, I’ve found that the calibration can be off by 0.002 ppm, which is a significant deviation. So while I do like this item, it may not be the most accurate option available.
I was using one for a few years, when I started getting funny readings. So recalibrated it, and it just wouldn’t hold anymore. It had been probably 3-4 years, so we had a good run together, but it just got me worried that it could stop being accurate at any moment, so instead of replacing it I went back to my handheld refractometer… where I started in this hobby!
4. Hanna Instruments Marine Monitor
I have actually not used this unit, but I love the idea of it. And it’s made by Hanna which has a strong track record in this industry.
Basically, you can monitor three things with this… well… monitor… temperature, pH, and salinity. It’s not a controller, so you can’t do anything with those values automatically. But, you can set audible alarms to alert you if something is wrong.
Now, who would want this? Well, this is certainly not the unit to use for making a fresh batch of seawater. This is meant to be a permanent fixture with your tank, to let you know when something is wrong. To be honest, salinity is rarely a problem in an established tank. But let me give you a personal example of how it can help.
I have an automatic water change system set up in one of my tanks. It uses a Neptune DOS to change out 5 gallons of water each week. A few weeks ago during my water change, I forgot to fill up the fresh seawater reservoir. Midway through the week, I checked on my ATO reservoir, and noticed it was almost empty. Strange, because it always lasts me an entire week. But I brushed it off since the weather had warmed up and I just figured the tank was evaporating a lot more.
Then during my weekly Friday maintenance, I noticed the reservoir was almost empty again, and this time I knew something was wrong. Sure enough, I had forgotten to refill the saltwater side of my automatic top off unit, so instead of refilling the tank with saltwater, it was topping off with RODI water. Luckily it was a fish only system and I caught it early so no harm done.
5. Refractometer
I’ve been using this refractometer for over five years now, and it has been consistently reliable since day one. I calibrated it when I first received it, and even after checking it periodically, it has never shown any deviation.
At such an affordable price, there’s no reason not to get this refractometer. Using it is a breeze – just place a few drops of saltwater on the measuring surface, put down the plastic top, and look through the viewfinder to find the reading.
The best part is, it works flawlessly, and the only maintenance required is to rinse and dry it after each use. It’s that simple.
Out of all the items on this list, if I had to choose one, it would undoubtedly be this refractometer. I wholeheartedly recommend it without any hesitation.
