To Salt or Not to Salt?
By: Cecilia Chen


The use of salt in freshwater tanks has recently been a controversial subject of some debate. This article is intended to give some objective information so that the beginner can make their own decision.

First off, some definitions. When we speak of “salt”, this is a confusing term, because salts are a large heterogeneous group that consists of any ionically bound elements or compounds. The salt that most freshwater aquarists mean to speak of, however, is NaCl (sodium chloride).

THIS SHOULD NOT BE CONFUSED WITH MARINE SALT, WHICH CONTAINS BUFFERS THAT ARE VERY HARMFUL TO MANY FRESHWATER FISH. Table salt is basically also NaCl, only with iodine added (the myth that iodized salt is harmful fish is largely false… iodine is a natural element that is needed in the diet of all fish, and is actually a supplement in many fish foods… the only thing in table salt of real harm to FW fish are the decaking agents, which are very low in concentration).



The reasons that some aquarists use salt in their FW tanks (usually at a concentration of 1 tablespoon / 5 gallons… do not confuse this with “brackishness” as this is a much lower concentration, and true brackish tanks use mostly other types of “hard” salts… see warning against marine salt, above) as a general preventative to disease are as follows:

  • Salt adds electrolytes, which reduce osmotic stress to the gills. This is especially important during disease, when the ability of the fish to maintain homeostasis with its surrounding water is disturbed.
  • Salt can aid in the production of the slime layer and speed up the healing of some wound sites. This occurs by hyperosmolarity… fish have a certain specific gravity (concentration of total dissolved solids) in their bodily fluids, and so does the surrounding water… if the surrounding water has a slightly higher concentration, the fluids from the wound site move into the water around it, and fresh plasma goes in to replace it, creating more blood flow in that area (makes it heal faster).
  • Many pathogens, such as Ichthyophthirius (the protozoan that causes “ick”), do not particularly like salt.



Despite some of its (rather minor) potential benefits, there are a lot of potential dangers to consider in using salt, especially if you are a beginner. Please make special note of these.

  • Although NaCl is not composed of any truly “hard” ions (laundering ions of Mg or Ca, which produce the hard water stains on your tank and are the only ions that count in true carbonate hardness), it does raise the total dissolved solids in the water… these add up to raise general hardness, or GH. 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. These fish include (but are not limited to) neon tetras, cardinal tetras, rummy nose tetras, hatchetfish, elephantnoses, and discus… in addition, most live plants will not tolerate it either. DO NOT USE SALT WITH ANY OF THESE FISH, AS SOME HAVE RATHER STRINGENT PH/KH/GH REQUIREMENTS, AND COULD DIE AS A RESULT OF THIS ADDITION. There are other Amazonian fish such as angelfish which will not particularly prefer salt, but may possibly tolerate it because they are hardier. Salt can also have an unpredictable effect on other fish, since there are no bodies of water in Nature which are naturally saline (high in NaCl) but very low in “true” hardness ion concentration (Mg, Ca, etc)… Rift African species, for example, need more than just ordinary “aquarium salt” (NaCl alone).
  • Salt, if not predissolved carefully, can give fish bad burns. This is especially true of scaleless fish, such as some types of eels and scaleless catfish.
  • The efficacy (effectiveness) of salt has not been proven experimentally to the satisfaction of many in the pet trade. Some swear by it, but many, as you can see, swear against it.

THE GENERAL RULE IN ANY TANK, ESPECIALLY THAT OF A BEGINNER, IS TO STEER CLEAR OF ADDING ARTIFICIAL ADDITIVES UNLESS ABSOLUTELY NECESSARY. Salt in many tanks is not… in a livebearer only tank (such as one with mollies, swordtails, guppies, or platys), I would consider recommending it (these are moderately hard water fish which like electrolytes in their water… some, such as the molly, from it’s Yucatan peninsula natural habitat, actually prefer it because they are semi-brackish), but since so many community tanks contain more delicate, soft water fish such as the neon tetra, I usually do not. Please consider all your fish carefully when setting up a tank environment, as harmony in a mini-ecosystem is extremely difficult to achieve and any one thing can throw it off. The (bolded) note on chemical additives goes not only for salt addition, but also for medications, pH up/down solutions, snail/algae eradicator, etc… if you are a novice and not entirely familiar with what you are adding, USE GREAT CAUTION, and educate yourself completely on the potential effects (some of which are unpredictable) of that product before you add it.


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