Aquarium salt is a common sight on pet store shelves. But isn’t salt just used in marine fish tanks? As it turns out, even freshwater tanks make good use of the product. So what are the uses of aquarium salt – and is it something you should have on hand?
What is Aquarium Salt?
Aquarium salt is the chemical compound NaCl – sodium chloride. It is the same salt that you add to your food for flavor and dietary needs. Fish don’t eat salt like we do. But it does serve a similar purpose in their bodies.
All salt comes from rocks in the Earth’s crust. As these rocks are broken down, salt is released into the environment, where it collects in aquifers, lakes, sediments, and the sea.
Salt for fish is the same as rock salt. Only it has been purified of silt and pollutants.
What Does Aquarium Salt Do?
One of the most important roles salt has in the bodies of organisms is that it helps balance water osmosis. Osmosis is how water flows from high to low concentrations across a membrane (a permeable barrier).
Body salt levels are balanced with care to either pull water from the environment (saltwater fish). Or to send it back into the surrounding water (freshwater fish).
Salt also helps regulate ion exchange across membranes, including the gills of fish. Fish release ammonia and carbon dioxide with the environment using their gills. Picking up oxygen in the process.
Last, salt stimulates the production of a thick slime coat in fish. The slime coat looks simple but it’s an important barrier against bacterial and fungal infections. It also speeds the healing of wounds taken from scrapes or fights.
Which is why you should never touch your fish with dry hands. The slime coat gets stripped away, leaving the sensitive, permeable skin naked to infections.
How Much Salt per Gallon for Saltwater Aquarium?
It is important to get the concentration of salt just right when setting up or doing water changes on a saltwater aquarium. Marine organisms are trickier to keep than freshwater ones because the sea almost never changes.
And when it does, any changes are very minute thanks to the massive water volume of the ocean. Even small but sudden variations in temperature, chemistry, and salinity are often fatal.
Most marine aquarium fish, corals, and invertebrates thrive at a specific gravity (salinity) of 1.020-1.025. Marine fish tend to be more flexible.
A standard salt mix for a saltwater aquarium should be added at ½ cup of aquarium salt per gallon of water.
Reef building corals and sea anemones often prefer a higher salinity. Most are found in shallow water where there is more sun for photosynthesis. The higher rate of evaporation in the shallows raises the salinity.
Wild-caught animals from the Red Sea, even the fish, also prefer a higher salinity (1.025-1.030). The Red Sea is not just shallow; it is surrounded by deserts on both sides with intense sunlight. Driving evaporation even faster.
To be certain that you have the salinity right, use a hygrometer. These devices measure the salinity of water with precision. Ensuring you won’t shock your sensitive pets with new aquarium water.
Salt in Aquarium Freshwater
It makes perfect sense to have salt on hand when doing water changes for a marine aquarium. But aquarium salt is also useful for freshwater setups.
All of the salt in the sea arrived there from rivers and streams. As rain, ice, and wind erode the land, mineral salts find their way into streams. Which become rivers, which then empty into the ocean.
Most rivers have trace amounts of salt, as a result. Mineral-rich lakes also exist when water sits over rocks packed with salts. Sodium chloride is the most common salt but other salts exist in lower amounts.
As a rough rule of thumb, fish that live in hard (mineral-rich), alkaline water do well with salt as a regular addition. These include many popular aquarium fish. Since tap water has carbonates in it already, a dash of aquarium salt will help these fish feel right at home.
Molly fish enjoy salt so much that it should be considered mandatory for them. You may even transition mollies over to pure seawater. They will live alongside clownfish and other reef fish.
Freshwater fish that thrive when you add aquarium salt:
- Molly fish
- Guppies
- Platies and Swordtails
- African cichlids
- Texas cichlids
- Convict cichlids
- Jack Dempseys
- Brackish water fish
- Most fish from hard, alkaline conditions
Not all fish do well with aquarium salt, though. Fish from soft (mineral poor), acidic conditions like parts of Southeast Asia and South America encounter little to no salt in the wild. They also prefer having any tap water treated to reduce its pH and hardness.
Salt is still a useful tonic for these fish. But half the dose for disease treatment. And don’t add salt to the main aquarium.
Freshwater fish that are sensitive to aquarium salt:
- Tetra fish
- Corydoras
- Loaches
- Spiny Eels
- Betta fish
- Gouramis
- Freshwater stingrays
- Most fish from soft, acidic conditions
How Much Aquarium Salt per Gallon?
As a general tonic, one tablespoon per five gallons is all you need. Assuming you don’t have any of the sensitive fish on this list.
Keep in mind that aquarium salt does not evaporate when added to a tank; it stays right where it is. So you need to account for the salt you add to the tank when topping it off or doing water changes. Adding more and more of it will make it too salty for freshwater fish.
Can I Use Sea Salt Instead of Aquarium Salt?
Yes, you can. Sea salt and aquarium salt come from the same source: evaporated sea water. Just be sure to read the ingredients label for any salt blend you choose. Cooking sea salt sometimes has anti-caking agents in it.
These soak up moisture from the air that will cause salt to harden in its container. Iodized table salt is also a no-go. Iodine does impact animal health, especially reef invertebrates. It is essential for aquatic pets but they get enough from their food. Those that don’t should be supplemented with care. Too much iodine is just as bad as too little.
All of these additives are unwelcome in your fish tank. But if you just need salt as a water tonic for your fish or for disease treatment? Then pure cooking sea salt works just as well.
That said, several aquarium salt blends contain additives that foster the growth of aquatic life. Marine aquarium salt, in particular, is better than cooking sea salt due to its high concentration of reef-building elements.
Treating Ich With Salt
Ich is a disease that looks like someone came by and dusted your fish with salt. Salt also happens to be a treatment for the parasite that causes ich.
A salt bath for fish isn’t recommended here. Ich is sensitive to salt during its free-swimming stage. Once it has a host, the ich parasite encapsulates itself in a protective coating that makes it resistant to aquarium salt.
You should treat the main aquarium with one tablespoon of salt per two gallons to kill free-swimming ich parasites. If you have sensitive fish from the list above, lower that to one tablespoon per five gallons.
Allow the salt to remain in the tank for a week, and then do your first water change. Be certain you don’t add fresh salt when refilling the tank.
Aquarium Epsom Salt Dosage
Epsom salt is magnesium sulfate; a very different chemical from sodium chloride. It is also found in nature, including in the ocean. Magnesium is an essential element for animals. Corals and coralline algae also use it in the construction of their skeletons.
Epsom salt is sometimes used as a tonic for internal fish diseases. Bloating disorders like dropsy, Malawi bloat, and swim bladder disease are improved with a brief bath.
A tablespoon of epsom salt in a gallon of aquarium water is all you need. Let the fish swim around in the heated bath for an hour. And then return it to the main aquarium.
Epsom salt is also useful for getting magnesium to freshwater plants. But most aquatic fertilizer blends are also enriched with magnesium. Use epsom salt if you want full control over what nutrients your plants receive.
Conclusion
Aquarium salt is an excellent tool in the kit of any aquarist. Its uses are obvious for marine fishkeepers. But freshwater hobbyists will still find it handy for helping sick fish recover faster.
FAQs
To treat the entire tank, use one tablespoon per 3 gallons of water. If your fish are not sensitive, you may up the concentration to one tablespoon per gallon. Increased over the course of 3 days rather than all at once. Use an antifungal agent like Melafix at the same time to eliminate body and fin fungus in aquarium fish.
Adding salt to fish tank needs to be done with care. Freshwater fish are often sensitive to even low levels of salt. Fish that are salt-hardy will still die if the salt concentration rises too fast.
