The question of how much salt per gallon in a saltwater aquarium is a common one, but, unfortunately, there isn’t a straightforward answer. Salinity, or the amount of salt dissolved in water, is very important, and it must remain constant.
Worrying about keeping your water chemistry balanced is difficult enough. Adding salinity to the mix is enough to keep dome freshwater tank overs away from saltwater. But one you understand a little more about aquarium salt, it isn’t such a difficult task.
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All about Salinity
Obviously, the main difference between a freshwater tank and a saltwater tank is the salt. Freshwater fish are easier to breed on fish farms, but most saltwater aquarium fish are caught in the wild.
For this reason, it’s important to mimic their environment as closely as possible. Stress is one of the hardest things for fish to deal with, and it’s the reason that so many fish die within days of being added to a new tank.
There are a lot of factors that contribute to stress. In any aquarium, you have to worry about the amount of space the fish have, whether they’re compatible with their tankmates, water chemistry, and oxygenation. In a saltwater tank, salinity is equally as important.
A more scientific explanation of salinity is that it measures the amount of sodium ions that are dissolved in the water. It’s expressed as part per thousand or ppt, but you need special equipment to measure it.
Specific gravity is an easier measurement to obtain, but you do have to invest in some additional equipment.
Hydrometer vs Refractometer
Both a hydrometer and refractometer measure specific gravity, but they work in different ways.
A hydrometer is the older of the two devices. To use it, you simply dip it in the water to collect saltwater from the tank, then place it on the counter. Then, a swing arm rises to indicate the specific gravity on an easy-to-read gauge. The higher the arm rises, the more salt is in the water, and the higher the specific gravity.
A hydrometer is an old favorite for some hobbyists, but it does have some downsides. Small bubbles in the water can affect the accuracy of the reading, and the moving parts wear over time.
The biggest downside to a hydrometer is that it doesn’t adjust for the temperature of the water, which is an important factor in determining specific gravity. Because of this, many people prefer to use a refractometer.
A refractometer measures the way the light bends as it travels through the water. The amount of salt in the water determines its density and affects the way the light flows through it.
Refractometers are much more accurate than hydrometers. The main reason for this is because refractometers correct for temperature differences, which makes them the primary choice for saltwater tank enthusiasts.
Of course, there are some downsides, too. Refractometers have to be calibrated regularly. While this is pretty easy to do, it is just another thing to add to the long list of things you already have to do to maintain your tank.
Another thing that may be a drawback to using a refractometer is that it requires a strong light source to work properly. Some models come with their own lights, but not always. Refractometers are also significantly more expensive than hydrometers, but they’re still affordable enough to fit into most budgets.
Things the Affect Salinity
The biggest factor that affects salinity is evaporation, which makes sense. As water evaporates, the salt stays behind, increasing the concentration that’s left in the water. By checking the specific gravity regularly, you can keep the salinity as constant as possible by countering for evaporation.
How Much Salt Per Gallon
Now that you know a little more about salinity and why it’s so important to keep it constant, you’re probably wondering how much salt you need to add to your tank per gallon.
Well, the short answer is until the specific gravity is between 1.020 and 1.023, though some say that a wider range of 1.017 to 1.028 is acceptable. The exact number depends on the type of fish you have in your tank.
Make sure you do your research to know what the ideal environment is for the fish that you chose. Lower salinity is good for tanks that are having issues with parasites. Higher levels are ideal for coral.
In most cases, you will need to add about ¼ cup of aquarium per gallon. Again, this isn’t a standard amount, you have to measure the specific gravity to be sure. Sometimes you may need to add more; sometimes, less.
How to Change the Salinity
The only way to appropriately increase the salinity of your tank is to remove some of the water and mix it with a marine mix. Of course, as mentioned, salinity rises naturally as the water in the tank evaporates.
To lower salinity, remove some of the saltwater from the tank and add fresh water to dilute the salt content.
Monitor and Adjust
Adding salt to an aquarium is not as complicated as you might think. With the right equipment and frequent testing, keeping the salinity within the right range is easy to learn.
Remember, generally, you will add ¼ of salt for each gallon of water, but that’s a general estimate. The only way to get it exactly right is to obtain the proper measurements.
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