There are three ways to test just how salty your water is:
And there is a fourth way, but I don’t recommend the tasting method (just not very accurate!)
The most accurate method, as well as the best value (in my opinion), is a refractometer. That’s why it is #1 on my list. For under $20, you can measure the salinity of your aquarium for the rest of your life. Rarely needs to be calibrated, and as long as you keep it clean it will likely last a lifetime.
If you are just trying to build a saltwater tank for the least amount of money possible, then go with the hygrometer. It will be accurate enough.
But sometimes accidents can happen, and the salinity of your tank can fluctuate unbeknownst to you. That is when you want a salinity probe. You will have to occasionally calibrate it, but that’s about it.
If you really want to get fancy, you can purchase the Neptune Apex, which comes with a salinity probe, and check on your tank from anywhere in the world. But that costs around $500, so I don’t recommend it!
5. Coralife Deep Six Hydrometer
Whereas the rest of the items on this list measure the salinity of water, this hydrometer measures the specific gravity. How it works is you fill the hydrometer with saltwater, and the plastic dial in the middle will float and point to a number. Specific gravity measures the density of the water, not the amount of salt.
While not the most accurate method, it will likely be accurate to within 0.001 ppm, which in the grand scheme of things, is accurate enough. Consistency is more important for your livestock than an exact number.
It is a bit of a pain in the butt to use this hydrometer, because you have to fill it with water, hold it steady, empty it, rinse it with freshwater, and let it dry. But it will save a few bucks and it works!
4. Milwaukee Seawater Digital Refractometer
This is a bit of a spendy option, but it is probably also one of the most accurate. All you need is a bottle of distilled water to calibrate, then use a pipette to put water into the tester, and you’ll get an immediate reading.
I would recommend this product if you are anal like me, and a total stickler for precision. Easy to use, easy to clean, and you can be confident you are getting the most accurate reading possible with the digital read-out.
Works on the same principal as the hand-held refractometer, just easer to read and a low probability of user error!
3. Hanna Instruments Waterproof Salinity & Temperature Tester
This is a pretty new item from Hanna Instruments. It is easy to use, easy to clean, and easy to calibrate. Just rinse if with RO/DI water after each use, and that’s it.
There are some drawbacks though. First off, you have to calibrate it once a month. Not a huge deal, but you have to buy their calibration packets and they run about $1.00 a piece.
The biggest drawback of this tester is it is not designed for tank water. It is designed to test freshly made saltwater. That’s a pretty big drawback in my opinion. But, if you are like most of us, you still use it to test your aquariums.
I’ve found that, after a month of use, the calibration can be off by 0.002 ppm, which is significant. So while I like this item, it is not the most accurate.
2. American Marine Pinpoint Salinity Monitor
This salinity monitor is awesome. You calibrate it occasionally (once every few months), and it will last for years. The digital display gives you a conductivity reading, which you can easily convert to specific gravity using a simple calculator.
There are a few downsides though. It’s not waterproof, so be careful. The probe is short, so you probably won’t be able to leave it in your sump and mount the display somewhere else. You can only mount this to a flat surface using velcro.
This is a nice item, highly accurate, but spendy. Honestly, if I was to go the probe route, I would probably just save up for a Neptune Apex so that I could monitor my tank at all times.
I’ve owned this refractometer for over five years now. I calibrated it once when I first got it. And I’ve checked it again from time to time, and it has never wavered.
For under $20, why not get this refractometer? Just place a few drops of saltwater onto the measuring surface, put down the plastic top, and look through the viewfinder to find the reading.
It works flawlessly, and the only maintenance is to rinse and dry it after each use. That’s it.
If I was to purchase one item on this list, it would be this refractometer. I recommend it without hesitation.