Mastering the Science of Salt Treatments


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Maintaining a healthy environment for your aquarium fish is paramount to their well-being, and sometimes that means turning to tried-and-true treatments like salt therapy. Salt treatment, also known as salt dip or bath depending on duration, can be an effective way to address various fish health issues. However, it requires precision and knowledge to ensure the right concentration and methodology. In this guide, we’ll delve into salt treatments, along the way we’ll be covering therapeutic concentrations, salinity testing, determining system volume, suitable scenarios, and the best types of aquarium salt to use.

Choosing the Right Scenario for Salt Treatment

While salt treatment can be beneficial, it’s important to recognize when not to use it. There are some scenarios where a salt treatment might be prudent, and others where I would avoid using salt.

Here’s some examples of scenarios where salt treatment might be a good decision:

      • Open Sores and Injuries: When fish have open wounds, a low-level salt treatment can help reduce osmotic stress. In freshwater, the fish have a higher salt concentration in their body than compared to the surrounding water. This means that they’re always fighting to keep these salts inside their body. By increasing the salinity of the surrounding water, you can reduce that osmotic stress, promote healing, and help to prevent secondary infections.

        • External Parasites: Certain external parasites, like Ich (Ichthyophthirius multifiliis) can sometimes be treated with salt alone, though a formalin treatment is going to have a greater degree of efficacy. A controlled increase in salinity can disrupt the life cycle of the Ich parasite, preventing its reproduction.

          • Bacterial Infections: Salt baths can help alleviate certain bacterial infections by creating an unfavorable environment for the bacteria while providing mild relief for the fish. This approach is often used alongside appropriate antibiotics.

            • Fungal Infections: Salt can help inhibit fungal growth and reduce the risk of fungal infections in wounded or stressed fish. However, it is important to note that true water mold is not as common as many retail aquarists might assert. Good pathology can help you easily make this determination.
            • Your system is experiencing a spike in nitrite (NO2) and fish are demonstrating distress. A very low concentration of salt is necessary to treat nitrite poisoning (50 mg/L); so a very low level salt treatment is all that is necessary to alleviate stress to fish due to elevated nitrite (any measurable reading.) Interestingly, the active ingredient in this treatment is the chloride ion, so calcium chloride would work equally well for this purpose.

          There are also scenarios in which I would not want to employ a salt treatment, even if some of the conditions above were present.

              • Sensitive animals: Some species originate from soft water that has a very low mineral content. It is not uncommon for those species to have an increased sensitivity to salt treatments.

              • Invertebrates: If you house invertebrates in your aquarium, including shrimps or snails, salt treatment might be dangerous.

              • Aquatic Plants: Salt is definitely detrimental to aquatic plants, and it should be avoided in tanks where aquatic plants are being kept.

              • Medication Interaction: If you are medicating your aquarium already, research the medication you’re using to ensure it is safe to use alongside a salinity treatment or the preparation you purchased doesn’t already contain salt.

            Understanding Therapeutic Salinity

            When considering salt treatments for fish, it’s a good idea to adhere to the therapeutic concentration of one to five grams of salt per liter (1-5 g/L). For species of fish with a known sensitivity to salt treatments such as scale-less catfish, Corydoras catfish, and some species of tetra.

            However, the salinity you choose on your salt treatment also depends on the length of time that you plan to treat the fish. Thus far we’ve discussed situations of salt treatments in what is referred to as a “prolonged bath” where the salt treatment goes on for weeks. However, in some instances, such as the treatment of bacterial disease Columnaris (cotton mouth disease), a short term high salinity bath might be prudent.

            In this instance you’d set up a hospital tank, preferably with your display tank water, and mix salt to 10-30 grams per liter for a period not to exceed 30 minutes. Shorten that duration to 10-25 minutes and use the lower end of the salinity spectrum for more sensitive species. This can be repeated daily depending on the strength of the fish and always remember to maintain adequate aeration.

            This range strikes a balance between its healing properties and its potential to cause stress to your fish. A concentration higher than this might cause undue stress, while a lower concentration could prove ineffective in treating the intended condition.

            How Much Salt Will I Need?

            Note that I’ve been citing salinity rather than specific gravity, a more commonly used metric in the retail aquarium trade to describe salt concentration . I’m doing this because salinity is simply a superior way to measure how much salt is in your water.

            Specifically, in this case I’m using salinity because it allows you to calculate how much salt you’ll need to reach the therapeutic range, rather than having to guess as you would have to do with specific gravity.

            Again, the therapeutic salinity for most aquarists employing a prolonged bath is about 3g/L, so this should probably be your goal value. This salinity value correlates to a specific gravity of 1.002 to 1.004 provided a typical 77F temperature for the water, and standard pressure.

            To determine how much salt you need to add for your system, simply multiply your system volume (in liters) by your goal salinity value, which will give you the number of grams of salt necessary to reach a therapeutic level.

            For example, if you have a 10-liter system you will need 30 grams of salt. (10 liters x 3 g/L = 30 grams)

            If you have a 100-liter system you will need 300 grams of salt. (100 liters x 3 g/L = 300 grams)

            Accurate salinity testing is a crucial step in ensuring the success of a salt treatment. A refractometer or hydrometer can be employed for this purpose and they are certainly an affordable and easy to use , but keep in mind that converting between specific gravity to salinity can be imprecise unless specific temperature and pressure considerations have been accounted for. It’s best to obtain a device that measures in salinity. You can also employ various types of probes that will provide improved precision in your salinity measurement, which may or may not, depending on your enthusiasm for calculations, be a required degree of precision in your salinity monitoring.

            Determining Volume in Liters

            The previous step was simple, if you already knew the volume of your system in liters. However, many people, including most Americans, have aquariums measured in gallons. Thus we have to take a step back and determine our system volume so that we can measure out our salt addition.

            If you know your aquarium volume, converting to liters is simple. There are 3.7854 liters per gallon. This implies that multiplying your gallon volume by that factor will provide you with the volume in liters.

            Thus, a 10-gallon aquarium has a volume equivalent to about 38 liters. (10 x 3.7854 = 37.854)

            A 55-gallon aquarium has a volume equivalent to about 208 liters. (55 x 3.7854 = 208.1967)

            You can also utilize this handy calculator to help you estimate your tank’s volume.

            If you don’t know your aquarium volume, or if you have a complicated multi-tank system, check out this recent blog on how to use a salt addition to determine the volume of water in your complex or uniquely-shaped system.

            Selecting the Appropriate Salt

            When choosing salt for your treatment, it’s important to opt for products specifically designed for freshwater aquariums. Marine salt mixes, like Instant Ocean for example, are typically used for marine aquariums and contain additional ions and alkalinity boosters that may not be suitable for freshwater fish. Do not add iodized table salt, or any other kitchen salt with additives such as yellow prussiate of soda (sodium ferrocyanide). Exposure of sodium ferrocyanide to sunlight generates hydrogen cyanide which can be highly toxic to fish.

            Technically any salt that is 100% sodium chloride will work, but in most circumstances it’s best to stick with aquarium salt from a reputable dealer.

            How Long Should the Salt Treatment Continue?

            As before, it does depend on the situation. If you are doing an Ich treatment, I would ensure that your salinity is elevated for a period exceeding the normal 7–14-day Ich life-cycle. A full 21-2ay (or more) treatment might be prudent in that instance.

            This is as compared to situations where you’re treating bacterial disease. In that instance you’re probably going to continue a salinity treatment in conjunction with some other mode of anti-biotic treatment. Similarly, with fungal treatments you’d probably continue the salinity treatment in conjunction with an acriflavine medication. In instances of injury or unknown lesion, the salinity treatment can continue as long as the fish is displaying open wounds.

            Most fish will tolerate a 1 g/L salinity concentration indefinitely, and a large plurality of fishes can tolerate 3 g/L indefinitely as well. However, in the interests of providing the best environment possible for your fish, salinity treatments should be discontinued once the health issues have subsided.

            Salt treatments can be a valuable tool in your arsenal for maintaining the health of your aquarium fish. By adhering to the recommended therapeutic concentration, accurately testing salinity, sizing your treatment system correctly, and selecting the appropriate salt, you can effectively address various fish health issues. Remember to always consider the specific needs of your fish species and their natural habitats before embarking on any treatment regimen. With proper care and knowledge, a digital scale, and a salinity probe, you can master the science of the salt treatment.


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