Salt Treatments: Chicken Soup for Your Fish
Salt is a safe, handy, and inexpensive way to treat many fish ailments.

By Myron Kebus, MS, DVM
Originally published in Water Gardening Magazine, Jan/Feb 1999   Reprinted with permission
Aquarticles

If I had to choose just one chemical to treat freshwater pond fish, it would be salt. Salt is probably the safest and the most forgiving of all the drug or chemical treatments available for our fish. It is highly effective in curing many types of diseases, infections, and conditions. And even if it won't cure everything that's ailing them, it will probably help ease them through the most difficult periods of their illness.

Treating Parasitic and Bacterial Infections
Salt treatments are effective in ridding pond fish of external parasites. Koi and goldfish may fall prey to several different parasitic infections, including Epistylis, Trichodina, Chilodonella, Dactylogyrus or Gyrodactylus. Pond fish that are infected with one of these parasites will typically engage in a behavior called "flashing," where the fish scrape themselves against the side of the pond and show signs of skin abrasions. It is best to obtain a skin sample and examine it under the microscope to determine whether external parasites are the cause of these symptoms. While awaiting clinical diagnosis, the fish may be effectively treated by using what is commonly called a "salt dip."

In a salt dip treatment, pond fish are placed, for a short period of time, in water that has a high concentration of salt (see sidebar for different types of salt treatments). External parasites that are attached to the fish are killed when they are exposed to the rapid increase in salt concentration. Because there is so much more salt in the water than there is in the parasite itself, the parasite dehydrates and its outer membrane collapses, much like a deflating balloon or an imploding building. The level of salt concentration is selected so that it will be toxic to the parasite, but not to the fish.

Salt is also effective in treating injuries or infections to the slime coat of our pond fish. The slime coat is the clear, mucous, outer layer of skin on the fish. It is a vital protective outer coating that wards off infection. It acts as a liquid band-aid covering over minor scrapes and bruises so that they can heal more quickly.

Fish can fall prey to a host of diseases, both parasitic and bacterial, that reduce the outer mucous layer. This, in turn, makes the fish much more susceptible to secondary infections and illnesses. Fish with an injured mucous layer sometimes look like they are wearing a fuzzy white coat. Other times, their coat looks dull, and may feel slimy or very dry. Although it's best to take a microscopic sample to determine the precise reason for the condition, it's not a bad idea to treat the fish with a salt bath until a definite diagnosis can been made.

A salt bath of less than half an hour or so will trigger the outer cells to become more active and secrete more mucous. Any excess or old mucous is sloughed off, as is any debris that has collected along the skin. As the slime coat is restored, the fish is more able to fight off the infection or disease affecting it.

A low-level salt bath also makes it easier for a sick or injured fish to maintain its internal body salts. Fresh water fish such as koi and goldfish live in a salt-free environment -- there is virtually no salt in the water around them. The fish's internal body fluids have low salt concentrations, around 0.7% or 0.9% salt. The fish must constantly work to maintain its internal body salt level. The less salt there is in the water around the fish, the harder it must work. If we add low levels of salt to the water, then the fish doesn't have to work so hard to maintain the necessary concentration of salt in its internal body fluids.

Salt also helps restore the mucous layer when it has been damaged by an exposure to certain potentially toxic chemicals, such as nitrite. Nitrite toxicity occurs when there is a build-up of this chemical from poor water quality. (See the detailed discussion of nitrite toxicity in the article "Don't Hold Your Breath," that appeared in the July/August 1998 issue of Water Gardening.) A salt bath of a brine solution that is approximately 2.5 lbs for every 100 gallons, for as long as the nitrite level is elevated, frequently for as long as many days, until the fish overcome the effects of nitrite toxicity.

Other secondary conditions that are commonly associated with skin problems may be helped, but not usually cured, by the use of salt. Ulcers are a common plague of koi and goldfish. Unless the ulcer is very mild, salt alone will not cure it. Nevertheless, a salt bath will probably restore some slime coat and help an affected fish hold on until more powerful treatments are implemented.

Drugs to combat parasitic and bacterial infections are also available to the hobby pond keeper, and several are just as effective as salt. Be careful not to use both salt and another treatment simultaneously. Serious harm can result to your fish. Formalin and potassium permanganate are frequently recommended to treat parasites, and both are valuable. The concurrent use of salt with either chemical can be very damaging, if not lethal. Goldfish are particularly prone to die if subjected to the combined use of Formalin and salt, although koi are less susceptible. Prudence suggests that salt be used either before, or after, a treatment with another chemical such as Formalin, potassium permanganate, or an anti-parasitic drug.

General Care and Maintenance
For years, both hobby and professional fish keepers have used very low salt water concentrations when moving their fish from one pond to another, or back and forth from a show. Salt is perhaps the single most important chemical for reducing transport stress in fish. Even extremely low amounts, such as 1.5 lbs for every 100 gallons, are beneficial to fish during period of transport stress.

Low levels of salt concentration are also used by fish keepers who maintain their fresh water fish in tanks or ponds where no biological balance is attempted. The low concentration of salt will help keep the fish healthy, warding off disease and infection, and keeping their slime coat in top condition. If the pond is equipped with biological filtration and some plant life, then there is no reason to keep a constant, low-level of salt concentration in the water. In fact, many plants will not tolerate salt in the water.

What Kind of Salt to Use
Salt comes in many different forms -- table salt or meat-curing salt, pickling salt, rock salt, solar salt, and water softener salt. Pond salt is also increasingly available, designed especially for treating illnesses in fresh water fish such as koi and goldfish.

Most sources recommend that fish be treated with non-iodized salt. Non-iodized salt includes commercially-available pond salt, as well as pickling salt or rock salt. Iodized table salt is frowned upon. There is a concern that long-term exposure to iodine can be toxic to koi and goldfish. In the field, I have not personally seen any evidence of iodine toxicity from the use of table salt to treat fish. By the same token, I do not know of studies that have confirmed the benefit of using iodized salt to treat fish. Good judgment suggests it would be best to avoid the possibility of iodine exposure. Use a salt that is not iodized.

Concerns are also being raised about the use of water softener salt to treat fish. Although it does not contain iodine, this kind of salt often contains anti-caking agents that prevent the salt from sticking and clumping together once it is exposed to humidity. One common anti-caking agent is yellow prussiate of soda (sodium ferrocyanide) When yellow prussiate of soda is exposed to sunlight, it generates hydrogen cyanide, which is considered highly toxic to fish. Having said this, I must add that many hobbyists have used water softener salt containing yellow prussiate of soda without causing ill effect to their fish. Just the same, it would be more prudent to use other forms of salt if they are at all available.

Solar salt is frequently used to treat pond fish. It is a non-iodized salt that is appropriate for salt dips and salt baths. As with all salts, review the label and ingredients to ensure that there are no anti-caking agents in the salt. Don't use epsom salt in place of non-iodized salt. Epsom salts are made of magnesium sulfate. This chemical compound cases fish to increase their bowel activity and expel the contents. It can cure constipation, which is a bigger problem in goldfish (1 tablespoon per quart for 10 to 15 minutes daily).

How to Measure Salt
Salt can be measured by weight, by volume, or by concentration. Measuring by concentration is by far the most difficult to understand. A 0.5% or 1/2% solution is about 4.2 lbs for every 100 gallons of water. In order to determine the solution, you must remember this equation and calculate how many pounds of salt it will take to reach the recommended concentration in whatever size tub or pond you are using. Luckily, there is an easier way.

Measuring by volume can be deceiving, since not all kinds of salt fill up a particular amount of space or volume. One cup of rock salt is not the same as one cup of table salt. A cup of coarse rock salt weighs about 230 grams. A cup of fine table salt weighs about 312 grams. The reason, of course, is that the finer grains of table salt allow for more salt to be packed into the one cup unit of measure.

When figuring how much salt to use, it's best to measure by weight, since it's the easiest to understand and to calculate correctly. All the different kinds of salt can be weighed, regardless of how much of it you can fit into a unit of measure such as a cup or a quart. Remember the old trick question, ‘Which weighs more, a pound of feathers, or a pound of stone?' A certain type of salt may fit in a smaller box, much like a pound of rocks, but still weigh just as much as a larger box of a different kind of salt, just like the pound of feathers.

How to Use Salt
Make sure you have a special "hospital tank" for the affected fish, and have an airstone running to make sure there is enough oxygen in the water in the treatment tank. Use water from your permanent pond to fill your treatment tank. It is important that the temperature and water chemistry be the same in both the treatment tank and the pond into which the fish will go after treatment. Any deviations between them will cause additional stress to the fish, making treatment more difficult and possibly negating any benefit from the salt treatment.

Once you have filled your treatment tank and determined how much salt you need, dissolve the salt in a bucket. Use water from the treatment tank to dissolve the salt. Make sure all the salt is dissolved and that you have a well-mixed brine solution. Pour the bucket of brine into the treatment tank and mix it well with the rest of the water in the tank. Then, add your injured or sick fish to the saltwater solution.

This is straightforward when you are only dissolving a small amount of salt to the treatment tank. It can be a challenge when you are trying to dissolve a larger quantity of salt. When you are dealing with larger quantities of salt, break it down into smaller portions so that each portion fits into a five-gallon bucket. Immerse the bucket gently into the water and carefully stir water into the bucket so that the salt slowly dissolves. Repeat this process until the full amount of salt is dissolved.

If you are salting a pond that has a waterfall, then you can use the effect of the waterfall to help dissolve the salt. Place the bucket of salt underneath the waterfall and allow the water to flow through the bucket. The brine solution will flush out and be continually replaced with fresh water.

Never, ever broadcast granules of salt directly into the pond. Sick fish sometimes sit on the bottom of the pond. Undissolved salt granules that fall to the bottom will burn the fish's skin. The salt can also damage and burn plants if the salt granules land directly on the plants or too close to them.

Never, ever put salt granules directly into the biological filter, or dissolve the salt so that its highest concentration is immediately drawn into the filter. The rapid increase in salt concentration will shock the bacteria and easily kill them. Bacteria are not so affected by salt if the saline concentration is very low.

Wind, Rain and Water Change
Weather conditions such as wind and rain can quickly change how much salt there is in a pond or water feature. Rain adds water to the pond and reduces the percentage of salt in the water. Use one of the many kinds of test kits available for determining the salinity of the water. Then add more salt to the water to restore it to the proper saline level.

Wind causes the pond water to evaporate, increasing the percentage of salt in the water. Again, the proper method is to test the salinity of the water, and then add more water until the proper saline level is reached.

If you do a water change, you also change the amount of salt in the pond. Salt is evenly distributed in the pond, so when you perform a water change you must proportionally return the salt to the pond. Determine how much new water you added to the pond, and then add enough salt to cause that new water to reach the proper salinity level. If you want to maintain a salt level of 2.5 lbs for every 100 gallons of water, and you removed 100 gallons from the pond, you would add back in 2-1/2 lbs of salt for that 100 gallons.

Salt Dips and Salt Baths
In a salt dip treatment, the injured or sick fish are exposed to a strong saline solution for short period of time, say up to 30 seconds or a minute. The generally recommended dosage is 2.5 lbs of salt for every 10 gallons of water (a 3% solution).

A salt bath is useful for treating fish in small tanks or in tanks that will be flushed out quickly. The fish are exposed to a moderate saline solution for up to 30 or 60 minutes. The generally recommended dosage is 1 lb of salt for every 10 gallons of water (a 1.2% solution).

The prolonged salt treatment lasts an indefinite period of time, perhaps even permanently. It involves adding salt to the pond water and maintaining that level of salinity for a matter of days, weeks, or months. This type of treatment is used to treat an underlying skin condition on a long-term basis after another type of treatment with salt or another chemical. The generally recommended dosage is 1.5 lbs of salt for every 100 gallons of water (a 0.18% solution).

When discussing the length of the salt treatment, we say "up to" a certain number of minutes because different fish have different tolerance levels, depending upon their size and their health. Smaller and weaker fish tend to be more sensitive. If the fish becomes very excited and swims around rapidly when you first place it in the salt treatment, you should weaken the solution and do the treatment for a longer period of time. If the fish stops moving and begins to look as though it is comatose, immediately remove it from the salt treatment and put it in a tank with fresh water. It will revive within a matter of minutes.