Salt for fish Health

So, I realized I need to get some numbers on here to help those who don’t think in metric to figure out how much salt to use per gallon and so on. Salt can help protect fish a little from nitrite so having 1 ppt of salt in a system during initial cycle up is a good idea if cycling with fish. Also 1-2 ppt of salt can be beneficial to many fish to help improve their slime coat and osmotic pressure. Most plants can handle 2 ppt of salt and even 3 ppt will only affect the sensitive plants like strawberries.

So here are some numbers to help people calculate how much salt would be needed for their systems.

4lb of salt per 100 gallons will give 5ppt

1000 lb of water is aprox 125 gallons

100 gallons is aprox 800 lb

1 lb of salt per 100 gallons = 1.25 ppt
1 lb of salt per 125 gallons = 1 ppt

Anyway 600 gallons and trying to get a level of 3 ppt of salt to help fish without hurting plants.

3 ppt divide by 1.25 ppt = 2.4 lb per 100 gallons to get the 3 ppt

2.4 lb salt times 6 = 14.4 lb of salt into my system to approach 3 ppt.

Now I just have to figure out how to measure out 14 lb of salt. Any ideas? (when I first wrote this, I didn’t have a kitchen scale to weight the salt.)

The salt to get is the sun dried pure water softener salt or pool salt. Generally the cheapest stuff they have. The smaller the crystals the easier it will dissolve but you really want to make sure it is not pelleted and you don’t want anything that removes iron or anything special like that. Just plain solar dehydrated sea water is what you are after.

It is important to dissolve the salt before putting it into a fish tank. If you have a sump tank with no fish in it, you may simply dump the salt in the sump. However, if you have no sump or there are fish in the sump, you will need to dissolved the salt in buckets of system water before pouring them into the system. This can take a while. If you have some means where you could run the water through a bin or bucket and let it waterfall back into the system, then tat would be much easier since the salt will sit on the bottom of the bin and having a continuous flow of less salty water will help it dissolve faster while still protecting the fish from the raw salt crystals. See the salt crystals will sit on the bottom of a tank and if a fish rests against it, they can get burned like a chemical burn.

General note here, I do not recommend salting a system on a regular basis. I grow channel catfish and they don’t like much salt so I make a point of leaving my systems unsalted except for when a health issue arises or, in the case of the quarantine system, I will salt that to 3 ppt when I get new fish. Nitrite spikes warrant salting to 1 ppt ASAP to help mitigate the nitrite toxicity to the fish. If you are cycling up a new system with fish, it would be reasonable to have that system salted to between 1-3 ppt, however if you will be doing water changes, you won’t be able to keep track of the salt level so you may wish to hold off salting until after the ammonia spike starts to go down at which point you need the salt to protect the fish from nitrite and it’s time to stop changing water anyway.

11 comments to Salt for fish Health

  • Frederickjh

    Any salt I hear will KILL strawberries in a system as they are salt intolerant or have your experiences with strawberries been different then the folks down under? Just wondering if you grow strawberries in Florida in your systems.

    • TCLynx

      I must admit that I’ve not done well with strawberries in my big system but that is probably more because the pH has always been really high due to the shells in my media. I’ve not yet tried strawberries in a system with a lower pH.

      Anyway, I’ve heard of people managing with low salt levels 1-2 ppt and growing strawberries and I’ve heard of other people saying the strawberries died at low levels and blame it on the salt but then again there are so many things that kill strawberries.

      Keep in mind that many people who use salt to treat disease often take it all the way to 6 ppt depending on the disease and type of fish. Channel Catfish won’t do well with salt that high so I’ve never gone that high on my salt levels.

      There are people who grow strawberries in Florida in aquaponics. I’ll try again some day.

  • Jon P

    Granular salt has about the same specific gravity as water, so you can volumetric liquid containers to measure salt weights, as in a pint weighs a pound, 8 lbs to the gallon, 40 lbs to the five gallon bucket. 14 lbs of salt, then, would be 14 cups, or 7 quarts.

    • TCLynx

      Well Jon, I think you might be able to go one way on that. You weigh the salt and see what size container you fill with that weight. However, since different size grains will be a different weight when filling a container I don’t think you can assume that any salt placed in a pint container will weigh a pound.
      Pool or water softener salt has really big crystals compared to table salt and since it is the pool or water softener salt we usually recommend for salting a system, I highly recommend using a scale to weigh it out since from one brand to another I’ve found vastly different size grains/crystals.

  • Jon Parr

    Uh, I fouled that up, having just read it again since I posted it. The last line should have read 14 lbs equals 14 PINTS equals 7 quarts. You may be right about granular size affecting weight/volume. I’ll dig out a scale and try it. Thanks for the info and hard work, TC

  • Glenn

    What do you think about this article?

    “Many fish stores, and other “sources of wisdom” about fishkeeping, will recommend salt as a general “tonic” for freshwater tropical fish. The usual suggested dosage of salt is something like a teaspoon per 5 gallons. As David A. Lass points out, there is not much therapeutic benefit at those dosages. “Salt serves more to assuage the hobbyist’s need to ‘do something’ for their tropical fish,” he writes. [8] There is absolutely no need to add salt to freshwater aquaria except as a specific treatment, and even here the sensitivity of certain fish species must be kept in mind. Fish health expert Dr Peter Burgess says he certainly doesn’t advocate salt for permanent use: “Unless the species has a natural requirement for salt, then we should not add salt to an aquarium (or pond).” [1]

    As the scientific data presented in this summary article indicates, adding salt to a freshwater aquarium on a regular basis will, at best, do nothing of any value at all. But at worst, it will stress salt-intolerant fish, making them more vulnerable to disease and less likely to live a healthy and normal lifespan. To understand why, we need to understand what salt does in water, and how fish are affected. But before this, we must clarify just what we mean by “salt.”

    Sodium chloride

    In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations (positively charged ions) and anions (negative ions) so that the product is electrically neutral (without a net charge) [Wikipedia, definition of “Salt (chemistry)”]. There are mineral salts for most minerals. But for the purpose of this article, we are dealing solely with common salt—what we know as table salt, or rock salt, or aquarium salt. This salt is a mineral that is composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of ionic salts. It is essential for animal life in small quantities, but it is harmful to animals and plants in excess. Marine salt has other minerals in it too, but it is still “salt” for the purpose of this discussion.

    Salt is an irritant, which causes the fish to secrete more mucus particularly in the gills where osmoregulation is occurring. And if salt is not predissolved carefully, it can give fish bad burns; this is especially true for scaleless fish, such as loaches, many catfish and some types of eels. [9]

    Salt makes the water denser than the same water without salt. The aquarium contains water. The bodies of fish and plant leaves also contain water, just as we do—humans are approximately 70% water. The water in the aquarium and the water in the fish/plant are separated by a semi-permeable layer which is the cell. Water can and continually does pass through this cell; fish do not “drink” because they don’t have to in order to take in water. When either body of water is denser, the other less-dense body of water will pass through the membrane to equalize the water on both sides. The fish must control this process through what is termed osmoregulation.

    Freshwater Fish Physiology

    Salt definitely interferes with the osmotic regulation of fish and plants. It should be left alone; nature regulated that part itself, by creating freshwater, brackish and saltwater fish. The vast majority of freshwater fish live in waters having no measurable salinity, and this has been crucial in the evolution of their physiology. Fresh water fish differ physiologically from salt water fish in several respects: their gills must be able to diffuse dissolved gasses while keeping the salts in the body fluids inside; their scales reduce water diffusion through the skin; and they also have well developed kidneys to reclaim salts from body fluids before excretion.

    Freshwater fish have physiological mechanisms that permit them to concentrate salts within their bodies in a salt-deficient environment; marine fish, on the other hand, excrete excess salts in a hypertonic environment. Fish that live in both environments retain both mechanisms. Freshwater fish concentrate salts to compensate for their low salinity environment. They produce very dilute but copious urine—up to a third of their body weight each day—to rid themselves of excess water, while conducting active uptake of ions at the gills. [2]

    The kidneys of freshwater fish have two functions: osmoregulation [discussed below] and hematopoiesis, which is the formation of blood celular components. Each fish species is adapted to the range of salts in its habitat water, and the kidneys function well within that range. The kidneys have to work harder whenever the salt content of the water in which the fish is living is greater than that of the fish’s preference, i.e., the natural habitat. The closer the water is to the species’ requirements, the easier it will be for the fish to maintain proper osmotic levels. One of the myths about the “benefit” of regular addition of salt is that it allegedly maintains an osmoregulatory balance; in point of fact, regular use of salt has the exact opposite effect and can cause bloating due to an osmotic imbalance. [3]

    Osmoregulation is the technical term for the physiological mechanism fish use to control the amount of salt and water in their bodily fluids. As the name suggests, it’s based on osmosis. Water is constantly passing through the cells of freshwater fish by osmosis in an attempt to equate the water inside the fish with the water in the aquarium. Freshwater fish regularly excrete this water through respiration and urination; the average fish will urinate 30% of its body mass every day. The more salt in the aquarium water, the greater the strain on the fish’s kidneys, which in turn adds to the fish’s stress in attempting to maintain their internal stability.

    And salinity affects the amount of energy the fish must spend to maintain the physiological equilibrium—the complex chain of internal chemical reactions that keep the pH of the fish’s blood steady, its tissues fed, and the immune system functioning. When salinity increases beyond what the fish is designed by nature to handle, the fish must work harder and use more energy just to “keep going.” Laura Muha [4] likens this to driving a car up a steep hill—it takes more energy (gas) to maintain the same speed as driving on level ground, and it causes more “wear and tear.” This increased energy output is wearing down the fish, and the fish is not able to expend this crucial energy on other important functions. The growth rate is affected, a shorter lifespan will usually result, and there will be increased risk of various health problems along the way.

    Fish and plants from mineral-poor waters do not appreciate being kept in slightly saline water conditions. Many of the most popular fish today, like Cardinal Tetra and rasbora, come from soft water habitats. Short term exposure to low salt concentrations across a few days or a couple of weeks may not do them major harm, but constant use of salt in their aquaria could cause problems. [5] In Weitzman et al. (1996), the authors mention that 100 ppm of salt is the maximum that can be tolerated by most characins, and some species show considerable stress leading to death at a level of 60 ppm. [6] To put this in perspective, 100 ppm is approximately equal to 0.38 gram of salt per gallon of water. One level teaspoon holds approximately six grams of salt, so just 1 teaspoon of salt in 16 gallons of water will cause stress, and in some species lead to death.

    Another problem is that salt increases the total dissolved solids [TDS] in the water. An aquarium treated with one teaspoon of salt per gallon of water will have an established dose of 2400 ppm. Add to this the TDS occurring from calcium and magnesium salts [these make water “hard”], water conditioners and other additives, and you can end up with over 3000 ppm of TDS. [10] This is intolerable for most fish; even the very hard water in the African rift lakes does not contain more than 600 ppm TDS. And for fish from naturally soft and acidic water environments, this is very dangerous, for nowhere in nature does acidic water exist with a level of TDS anywhere near this. And the deviation from normal osmotic pressure that this creates is very harmful to all fish.

    Keeping the tank salty all the time will not help with disease resistance in freshwater fish; in fact, it will actually increase the fishes’ susceptibility to disease and parasites by keeping the fish somewhat stressed all the time, and this weakens the immune system. And at the low level of salt generally recommended for these so-called benefits, there will be no benefit that cannot be achieved solely with regular water changes using a good conditioner.
    Using salt to increase water hardness

    Although plain aquarium/tonic salt (sodium chloride) is sometimes suggested as a good way to increase hardness and improve buffering, it in fact provides very little of either. Marine salt mix, on the other hand, will raise the pH and carbonate hardness quite significantly. But it also raises the salinity, something most freshwater fish do not appreciate. If you live in a soft water area and want to keep hard water fish, using marine salt mix is not really a viable option. Rift Valley cichlids, in particular, seem to be peculiarly sensitive to salt, and elevated salinity levels have been identified as one factor responsible for the dropsy-like disease known as Malawi Bloat (Andrews, et al. 1988). [7]

    Fish lore also has it that salt is good for use with mollies, other livebearers and Goldfish. David Lass [8] notes that the vast majority of livebearers, including mollies of all types and colors, and sailfins, come from the Far East. They have been raised for generations in water that is moderately hard, and of neutral pH. These tropical fish are very far removed from the wild mollies that came from brackish water. All of the sailfin and lyretail mollies, balloon bellies, blacks, reds, and dalmations do fine without salt. The same with Goldfish. The main confusion is that tropical fish need alkalinity. Salt is just one part of alkalinity.

    Although NaCl is not composed of any truly “hard” ions, it does raise the total dissolved solids in the water, and these contribute to raise general hardness. This is not well tolerated by a number of fish, especially true softwater fish from places like the Amazon River basin, where there are very few electrolytes of any kind in the water. Salt can have an unpredictable effect on softwater fish, since there are no bodies of water in Nature which are naturally saline (high in NaCl) while being very low in “true” hardness ion concentration (calcium, magnesium, potassium, etc.). [9]

    Salt and Plants: When salt is added to the aquarium water, the water inside the plant cells is less dense so it escapes through the cells. The result is that the plant literally dries out, and will wilt. I’ve so far been unable to find a measurement of how much salt will be detrimental to plants; all authorities I have found do note that some species are more sensitive than others, and all recommend no salt in planted aquaria.

    Domestic water softeners: Domestic water softeners do not produce soft water in the sense that aquarists mean. What domestic water softeners do is remove the temporary hardness (such as carbonates) that potentially furs up pipes and heaters by replacing it with permanent hardness (such as chlorides) that does not. While you can pass this softened water through a reverse-osmosis filter to remove the permanent hardness as well, until you have done so, you shouldn’t consider the softened water as being suitable for soft water fish.

    In fact, aquarists are divided on whether the resulting softened water is safe for keeping fish at all. The odd balance of minerals in softened water is not typical of any of the environments from which tropical fish are collected. While the chloride levels are much higher than those soft water fish are adapted to, the levels of carbonate hardness are too low for the health of hard water fishes like Rift Valley cichlids, Goldfish, and livebearers. So the safe approach is not to use it in any aquarium, and instead draw water from the unsoftened drinking water source in the kitchen. [7]

    Read more:

    • TCLynx

      Wow that is quite the article.

      Please keep in mind that most of us doing aquaponics don’t use salt regularly. Usually only to treat particular problems (like protecting fish from a nitrite spike or with new fish just moved or fish exhibiting a disease or parasite attack.) So it isn’t like the salt level is being allowed to simply rise and rise from continued additions of salt. That said, the tilapia many people use in aquaponics are actually quite able to handle salty water but bluegill and Channel catfish are far more sensitive to salt I my experience with channel catfish is that I will only do salt over 3 ppt for a short bath for them. I might salt a system to 3 ppt when I get new fish but otherwise the salt levels are allowed to fall back near 0 over time.

      Since most aquarium medications are not safe to use on fish meant for human consumption nor would they be safe to use in aquaponics where we are also eating the plants, we are generally left to rely on salt as the only food safe treatment for the fish.

      While there are some plants that can tolerate higher levels of salt, I don’t know of many aquaponic veggies that would do well with even 6ppt for long. Luckily most of us doing aquaponics are not going over 3 ppt of salt very often and most veggies can handle 3 ppt though some sensitive plants like strawberries don’t do well with salt levels that high.

      The biggest problem with salting a system is that without special test equipment, you can’t tell accurately what the salt level is at so it becomes dangerous to repeatedly salt a system since that can cause elevated salt levels that are problematic.

    • Eden Growing

      Very nice article! Thank you!

  • David

    GREAT blog post and responses. As always, hurray TCLynx for excellent information on channel cats and AP in general. FYI I use an inexpensive ($20) refractometer to monitor salinity. It works well though the reading is very low on the 0 to 100 ppt scale.

    TCLynx I am very interested to know what you have experienced regarding channel catfish and stress due to salt. I have quarantined cats for 10 days or more at 5ppt+ and my AP system is 2-3ppt for extended periods sometimes. I may be overlooking the signs, but the cats seem to be fine. Though based on the above post I will decrease salt to 1ppt or less over time.

    • TCLynx

      It may depend somewhat on the conditions your catfish came from and what they are used to. I do know that I have salted before and they seemed to flash and be stressed out when the salt level was above 3 ppt but mine are used to salt levels that are very low.
      Keeping your system at 2-3 ppt of salt may make it hard to grow some sensitive crops that don’t like such a high sodium or chloride level (like strawberries.)

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