When in Doubt - Salt  by Terry Cusick

There is something wrong with your fish. You've checked all the water quality parameters, pH, ammonia, nitrite, nitrate, heavy metals, chorine, and DO, and they're all OK. You observed the fish swimming and it does not have swim bladder problems. You've physically examined the fish for the visible crustacean parasites, fish lice (Argulus), anchor worm (Lernea), and gill maggots (Ergasilus). The body is not swollen, there are no ulcers or wounds, the abdomen is firm, the vent looks normal, and the gills are smooth and regular with a consistent red color. You've now run out of things to check and you haven't discovered what the problem is. At this point, the natural tendency is to want to do something, so you guess at what might be wrong. You treat for what ever you think is wrong with some chemical concoction. When that doesn't work, you try another concoction and another until the fish die. Flying blind just doesn't work unless you are extremely lucky. Try salt - it is affective against lots of ailments and at the very least it will buy you time to get help.


Salt is a wondrous mineral for most fish including goldfish and koi. Salt has the following benefits:

First of all it is safe. You can get the dosage off by quite a bit and not harm your fish. I know of no one that has killed their fish by treating them with salt. I can not make that claim with any other type treatment. The only downside to using salt is that you lower minutely the capacity of water to hold dissolved oxygen. Known as the DO Saturation Point of water.
It relieves Osmoregulation and boosts the fish's immune system. Fresh water fish are bags of salt water swimming around in unsalted water and their gills are a permutable membrane. Remember in high school science class when they talked about this. It was called osmosis. You were probably thinking at the time, "When will I ever use this knowledge". This is it! Two unequal solutions separated by a permutable membrane will tend to equalize. So the fish have to work hard, very hard, to retain their salt. This work is called Osmoregulation. By adding salt to the water, you relieve the fish of some of the energy that it expends on osmoregulation and they can use this extra energy to boost their immune system. It is a good idea to add a 0.1 % salt solution to your quarantine tank for new or sick fish. Especially if the fish has an ulcer or open wound. Imagine how hard it would be to retain its salt with a big hole in its side.
It blocks the affects of nitrite in the water. Nitrite in your fish's water is absorbed into the fish's blood stream, turns the blood brown, and lessens the blood's capacity to carry oxygen to all parts of the body. This is called "Brown Blood Disease". Salt some how blocks the absorption of nitrite.
It kills all the protozoan parasites including ich. Since we have already addressed the Crustacean Parasites which we can see with the naked eye, Argulus, Lernea, and Ergasilus, this only leaves the flukes which we will talk about later.
Salt is easy to find and buy. In addition, it is affordable for large systems.


The salt you use is pure salt, not salt with additives like table salt that contains iodine. You can find it in pet stores sold as Aquarium Salt or in large bags of rock salt without additives used for water softeners in super markets and home improvement stores. Make sure the salt you buy is 99.9% salt (Sodium Chloride or NaCl). Usually, salt treatments are described as a percentage of salt in the water. 0.1 percent (that is zero point one percent or 1 part per thousand) is approximately one pound of salt per 100 gallons of water or one teaspoon per gallon. Because the one teaspoon is by volume and not by weight, you can only use the more finely ground aquarium salt and not the rock salt for this method of measurement. The normal dosage is 0.3 % for almost everything. There are two exceptions. If you want to relieve stress because you're transporting your fish or introducing them to a new environment you should place them in a 1% salt solution. A salt tolerant strain of trichodina has been discovered in the last few years. So if your fish have tichodina, assume it is the salt tolerant kind and increase the salt to a 0.6 % solution. Before you start adding the salt, change out about 50% of the water. You should then add the salt at a rate of 0.1 % every 12 hours until you reach the desired level. For example, if you have a 100 gallon system and you want a 0.3% salt treatment, you would add 1 pound of salt at 8 AM , another pound at 8 PM , and the final pound the next morning at 8 AM . If you are losing fish, you may want to consider shortening this period. For water changes, figure you are replacing the same percentage of salt as you do water. So, using the same previous example, if you want to do a 25% water change, you would remove 25 gallons of water. Since you started with 3 pounds or 48 ounces of salt in the water, you need to replace 25 % of this salt or 12 ounces. I dissolve this in a 5 gallon bucket of water with an air stone ahead of time and then add it to the balance of the replacement water at the time of the water change.  There are meters that read the amount of salt in the water. Every club should own one because with water changes, it is easy to make a mistake and the meter makes sure you are maintaining the salt level. A good one costs around $75.


Some fish keepers keep their fish in salt all the time, a practice I would not recommend. Using this method, the fish's ability to osmoregulate atrophies and there is no benefit to adding salt when the fish is ill. In addition, it is believed that because of this practice, the salt tolerant trichodina came about.


Where do you go from here? If you did all the things we talked about at the beginning of this article and it was done correctly, your fish more than likely have one of the microscopic parasites that afflict fish, but which one? The salt will kill most of these and will boost their immune system so they can fight off the affects of the others, but without knowing what's attacking them; your fish are still at risk. You need a microscope and someone who knows how to use it and can identify the parasites that infect fish. A microscope is another one of those things I think your local club should buy and have available for its members.


If you can't get a microscope or someone who knows how to use it, then increase the salt in your system to 0.6 % and continue the treatment for 3 weeks minimum. Also, treat for flukes. I would use fluke tabs for small systems and potassium permanganate (PP) for larger ones. Treat your system 3 times 4 days apart if the temperature of the water is in the 70's. The PP treatment is very dangerous to your fish if not done right, so it is a good idea to get someone who has done it before and can help you.


In conclusion, when your fish are in trouble and you're not sure what to do, add salt to your aquarium or pond. It is safe for your fish, it will improve their situation in varying degrees depending on what is wrong, and most importantly, it buys you time to figure out what is wrong and get help.