The addition of salt to the freshwater (FW) aquarium remains a persistent source of controversy. One need only perform a thread search at Aquaria Central to find numerous recommendations for or against its casual use.
Those who add salt cite observed health benefits, and typically have had no untoward events after years of use. For others, the efficacy of salt has not been sufficiently proven . In light of certain potential risks or a previous negative experience, they elect not to add salt unless medicating for a certain condition.
This thread includes widely accepted and objective information on the topic of salt addition in the FW aquarium. It concludes with the OP’s personal opinion on the topic. I apologize for the length and technical nature of the post but it is necessary to establish some of the biology/chemistry behind salt’s benefits and potential harm.
It is important to note that this discussion is geared for the addition of salt to specimen tanks that would not ordinarily promote higher salinity. Brackish/semi-brackish live bearer tanks or those that inherently require higher levels of general hardness (GH) including African Rift Lake cichlids merit their own discussion. The GH needs of African cichlids require a salt balance above and beyond those provided with the addition of plain salt (e.g. “hard” magnesium provided by Epsom salt). Recall that there are no naturally occurring aquatic environments which have high sodium salinity with simultaneously low hardness due to low calcium and magnesium ion concentrations.
The addition of sodium chloride (table or commercially available products marketed for aquarium use) typically at a concentration of 1 tablespoon per 5 gallons of water has been promoted to create several benefits for fish specimens including (with OP's embedded counterpoints):
Inhibition of nitrite toxicities: Salt can minimize nitrite poisoning by inhibition of nitrite ion uptake if chloride concentration is ~30 times greater than that of nitrite by sequestration of anion binding membrane transport. Assuming a toxic nitrite level of 0.1 ppm, this would require an estimated chloride concentration of ~3 ppm. Counterpoint: A mere 1 teaspoon of salt would be sufficient to provide this desirable effect for ~300 gallons of tank water; contrast this to the typical recommendation for added salt per gallon.
Reduction of osmotic pressure and stress: The addition of salt electrolytes can reduce osmotic stress for the gills. The ability of the fish to maintain homeostasis with its surrounding water is disturbed during times of stress or disease. Equilibrating this gradient provides ‘relief’ for specimens. The osmotic pressure in question is not ion specific and is comprised of the total ionic potential of a many ions in solution including magnesium (Mg), calcium (Ca), chloride (Cl), sodium (Na), potassium (K), etc. Counterpoint: The sodium and chloride contribution of salt addition represents only a fraction of the total osmotic potential for tank water of average tank hardness (i.e. GH). Mg and Ca are far more important in this pressure system than either Na or Cl. Excessive gradients can lead to disruption of membrane potentials for specimens both at the gill membrane and at other ionic exchange membranes. Finding this balance is difficult.
Promotion of slime coat and wound healing: Salinity promotes the creation of slime coat in many fish. This coat assists in the clearance of scale-bound parasites and helps cope with other disease states. Counterpoint: Many (if not most) commercially available water conditioners already provide for stimulation of this coat. Wound healing may occur via the created osmolar gradient. If the surrounding water has a higher concentration of total dissolved solids (TDS) than the fluids circulating within the fish, fluids move away from the wound site. Fresh plasma moves in response to the displacement, promoting flow to the wound area and augmenting immune response via migration of immune cells to site of injury. Counterpoint: There is also a concomitant risk of osmotic stress directly across already fragile and friable fish tissue membranes if the TDS osmolar gradient is too large. This is especially dangerous in the context of the high TDS ‘salt bath’. Plasma seepage or hemorrhage can occur in extreme cases as a result of tissue disruption (just as it can in humans).
Medicinal additive to promote clearance of protozoan diseases: Many pathogens including Ichthyophthirius do not tolerate higher concentrations of salinity. In conjunction with an increase in temperature to accelerate the protozoan’s life cycle, increased salinity is often all that is necessary to turn the tide against the disease. Salt is a welcome ally in the war against dreaded “white spot” and in this configuration, is treated as a medicinal additive. Appropriate treatment regimens also call for large water changes to remove this excess salt upon conclusion of the treatment. Note that in this context salt is used as a ‘medicine’, not as a regular tank additive.
Despite the potential benefits, there are considerable dangers associated with the regular addition of salt to the FW aquarium and especially with the use of higher concentration salt baths.
Salt may have an unpredictable effect on many specimens; some fish seem unaffected by its addition while others show instant signs of irritation. If not predissolved before addition, salt can generate serious burns. This is an important consideration for scaleless fish including certain species of loach, catfish and freshwater eels.
As mentioned, sodium chloride raises the total dissolved solid (TDS), GH and the important osmolar gradient of water. For those with average general tank hardness, this addition is less significant due to the presence of the other TDS ions previously listed (specifically Ca and Mg). However, for those with softer tank water, the addition of salt can have a profound impact. Many fish specimens generally do not thrive in waters of higher TDS including wild-caught (and to a lesser extent tank-raised) fish from the Amazon basin. Discus, tetra, corydoras etc. owners should be aware of this dynamic. FW fish are adaptable creatures but immersion in too high (or too low) TDS can have serious consequences for certain species. A further discusion on this topic was recently discussed (at AC.com) here:
http://www.aquariacentral.com/forums/showthread.php?t=167821&highlight=great+post+TDS
It is difficult for the average aquarist to create a balance between an osmolar gradient that will assist the fish vs. one that can actually promote stress. Inherent variability from one species to another (even one specimen to another) also means that a single recommendation for level of ‘therapeutic salt’ is impossible to establish. Salt baths (with much higher added salt concentrations) place fish in environments of increased TDS and GH for brief periods of time. This is an inherently stressful event for an already stressed specimen. Such baths are promoted by some for the treatment of edema (aka ‘dropsy’). The renal (kidney) and hepatic (liver) failure often associated with this condition makes the fish especially susceptible to imbalances in osmotic regulation; if the bath itself helped to alleviate some of the edema, the switch back to regular tank water (at lower TDS) in itself represents another environmental challenge. The primary goal should be to treat the underlying cause (e.g. bacterial infection) whenever possible and not to merely palliate manifestations or symptoms of the disease. We all strive for consistency in the aquatic environment whenever possible.
Most live plants do not appreciate the increased salinity of excess sodium. This is the reason that soft water conditioners (using NaCl salts and KCl) are discouraged for planted tank use. Those with certain invertebrates (snails in particular) may also attest to the unfortunate results of persistent increased salinity.
You regularly see a philosophy shared among posters throughout these forums: the principle of not adding any conditioners/substances to water unless required for specimen health. An antibiotic is never added ‘for the heck of it’ but rather to combat a specific condition. In contrast, water conditioner is a proven life-saving additive to neutralize the presence of deadly chlorine and chloramines. It has also been laboratory tested for safety even in ‘overdose’ quantities. Epsom salt, baking soda, crushed coral, aragonite or cichlid salts are proven to provide the GH needs for African Rifts. The use of pH buffers and algaecides are almost unilaterally discouraged. In this OP's estimation, there is little compelling evidence supporting or validating the introduction of salt (or salt bath) for anything other than a recognized medicinal purpose (e.g. protozoal disease). There are no existing guidelines for its safety or efficacy. There is no compelling evidence strongly in support of its addition (nor are there any situations calling for its absolute contraindication).
It is this OP's belief that the regular use of salt in the aquarium may be associated with disproportionately more harm than good. Striking a balance between potentially beneficial osmolar gradients versus those capable of promoting fish injury is difficult, is subject to inter-species variability, and represents additional stress for the specimen in the context of a high TDS bath. Salt addition should be treated as a welcome medicinal in the arsenal against disease; not as an additive for an otherwise stable aquatic environment.
Many will continue to use salt regularly in their FW aquariums with no problems (perceived or otherwise) or to augment other disease treatment regimens. We see wide variability in aquarists and in their habits/beliefs; what is acceptable for one aquarist is not univerally acceptable for the other. At the end of the day, we all seek to provide exceptional care for our tank inhabitants. For those seeking information on salt, I hope this serves as yet another voice in the crowd.
Whew….
Those who add salt cite observed health benefits, and typically have had no untoward events after years of use. For others, the efficacy of salt has not been sufficiently proven . In light of certain potential risks or a previous negative experience, they elect not to add salt unless medicating for a certain condition.
This thread includes widely accepted and objective information on the topic of salt addition in the FW aquarium. It concludes with the OP’s personal opinion on the topic. I apologize for the length and technical nature of the post but it is necessary to establish some of the biology/chemistry behind salt’s benefits and potential harm.
It is important to note that this discussion is geared for the addition of salt to specimen tanks that would not ordinarily promote higher salinity. Brackish/semi-brackish live bearer tanks or those that inherently require higher levels of general hardness (GH) including African Rift Lake cichlids merit their own discussion. The GH needs of African cichlids require a salt balance above and beyond those provided with the addition of plain salt (e.g. “hard” magnesium provided by Epsom salt). Recall that there are no naturally occurring aquatic environments which have high sodium salinity with simultaneously low hardness due to low calcium and magnesium ion concentrations.
The addition of sodium chloride (table or commercially available products marketed for aquarium use) typically at a concentration of 1 tablespoon per 5 gallons of water has been promoted to create several benefits for fish specimens including (with OP's embedded counterpoints):
Inhibition of nitrite toxicities: Salt can minimize nitrite poisoning by inhibition of nitrite ion uptake if chloride concentration is ~30 times greater than that of nitrite by sequestration of anion binding membrane transport. Assuming a toxic nitrite level of 0.1 ppm, this would require an estimated chloride concentration of ~3 ppm. Counterpoint: A mere 1 teaspoon of salt would be sufficient to provide this desirable effect for ~300 gallons of tank water; contrast this to the typical recommendation for added salt per gallon.
Reduction of osmotic pressure and stress: The addition of salt electrolytes can reduce osmotic stress for the gills. The ability of the fish to maintain homeostasis with its surrounding water is disturbed during times of stress or disease. Equilibrating this gradient provides ‘relief’ for specimens. The osmotic pressure in question is not ion specific and is comprised of the total ionic potential of a many ions in solution including magnesium (Mg), calcium (Ca), chloride (Cl), sodium (Na), potassium (K), etc. Counterpoint: The sodium and chloride contribution of salt addition represents only a fraction of the total osmotic potential for tank water of average tank hardness (i.e. GH). Mg and Ca are far more important in this pressure system than either Na or Cl. Excessive gradients can lead to disruption of membrane potentials for specimens both at the gill membrane and at other ionic exchange membranes. Finding this balance is difficult.
Promotion of slime coat and wound healing: Salinity promotes the creation of slime coat in many fish. This coat assists in the clearance of scale-bound parasites and helps cope with other disease states. Counterpoint: Many (if not most) commercially available water conditioners already provide for stimulation of this coat. Wound healing may occur via the created osmolar gradient. If the surrounding water has a higher concentration of total dissolved solids (TDS) than the fluids circulating within the fish, fluids move away from the wound site. Fresh plasma moves in response to the displacement, promoting flow to the wound area and augmenting immune response via migration of immune cells to site of injury. Counterpoint: There is also a concomitant risk of osmotic stress directly across already fragile and friable fish tissue membranes if the TDS osmolar gradient is too large. This is especially dangerous in the context of the high TDS ‘salt bath’. Plasma seepage or hemorrhage can occur in extreme cases as a result of tissue disruption (just as it can in humans).
Medicinal additive to promote clearance of protozoan diseases: Many pathogens including Ichthyophthirius do not tolerate higher concentrations of salinity. In conjunction with an increase in temperature to accelerate the protozoan’s life cycle, increased salinity is often all that is necessary to turn the tide against the disease. Salt is a welcome ally in the war against dreaded “white spot” and in this configuration, is treated as a medicinal additive. Appropriate treatment regimens also call for large water changes to remove this excess salt upon conclusion of the treatment. Note that in this context salt is used as a ‘medicine’, not as a regular tank additive.
Despite the potential benefits, there are considerable dangers associated with the regular addition of salt to the FW aquarium and especially with the use of higher concentration salt baths.
Salt may have an unpredictable effect on many specimens; some fish seem unaffected by its addition while others show instant signs of irritation. If not predissolved before addition, salt can generate serious burns. This is an important consideration for scaleless fish including certain species of loach, catfish and freshwater eels.
As mentioned, sodium chloride raises the total dissolved solid (TDS), GH and the important osmolar gradient of water. For those with average general tank hardness, this addition is less significant due to the presence of the other TDS ions previously listed (specifically Ca and Mg). However, for those with softer tank water, the addition of salt can have a profound impact. Many fish specimens generally do not thrive in waters of higher TDS including wild-caught (and to a lesser extent tank-raised) fish from the Amazon basin. Discus, tetra, corydoras etc. owners should be aware of this dynamic. FW fish are adaptable creatures but immersion in too high (or too low) TDS can have serious consequences for certain species. A further discusion on this topic was recently discussed (at AC.com) here:
http://www.aquariacentral.com/forums/showthread.php?t=167821&highlight=great+post+TDS
It is difficult for the average aquarist to create a balance between an osmolar gradient that will assist the fish vs. one that can actually promote stress. Inherent variability from one species to another (even one specimen to another) also means that a single recommendation for level of ‘therapeutic salt’ is impossible to establish. Salt baths (with much higher added salt concentrations) place fish in environments of increased TDS and GH for brief periods of time. This is an inherently stressful event for an already stressed specimen. Such baths are promoted by some for the treatment of edema (aka ‘dropsy’). The renal (kidney) and hepatic (liver) failure often associated with this condition makes the fish especially susceptible to imbalances in osmotic regulation; if the bath itself helped to alleviate some of the edema, the switch back to regular tank water (at lower TDS) in itself represents another environmental challenge. The primary goal should be to treat the underlying cause (e.g. bacterial infection) whenever possible and not to merely palliate manifestations or symptoms of the disease. We all strive for consistency in the aquatic environment whenever possible.
Most live plants do not appreciate the increased salinity of excess sodium. This is the reason that soft water conditioners (using NaCl salts and KCl) are discouraged for planted tank use. Those with certain invertebrates (snails in particular) may also attest to the unfortunate results of persistent increased salinity.
You regularly see a philosophy shared among posters throughout these forums: the principle of not adding any conditioners/substances to water unless required for specimen health. An antibiotic is never added ‘for the heck of it’ but rather to combat a specific condition. In contrast, water conditioner is a proven life-saving additive to neutralize the presence of deadly chlorine and chloramines. It has also been laboratory tested for safety even in ‘overdose’ quantities. Epsom salt, baking soda, crushed coral, aragonite or cichlid salts are proven to provide the GH needs for African Rifts. The use of pH buffers and algaecides are almost unilaterally discouraged. In this OP's estimation, there is little compelling evidence supporting or validating the introduction of salt (or salt bath) for anything other than a recognized medicinal purpose (e.g. protozoal disease). There are no existing guidelines for its safety or efficacy. There is no compelling evidence strongly in support of its addition (nor are there any situations calling for its absolute contraindication).
It is this OP's belief that the regular use of salt in the aquarium may be associated with disproportionately more harm than good. Striking a balance between potentially beneficial osmolar gradients versus those capable of promoting fish injury is difficult, is subject to inter-species variability, and represents additional stress for the specimen in the context of a high TDS bath. Salt addition should be treated as a welcome medicinal in the arsenal against disease; not as an additive for an otherwise stable aquatic environment.
Many will continue to use salt regularly in their FW aquariums with no problems (perceived or otherwise) or to augment other disease treatment regimens. We see wide variability in aquarists and in their habits/beliefs; what is acceptable for one aquarist is not univerally acceptable for the other. At the end of the day, we all seek to provide exceptional care for our tank inhabitants. For those seeking information on salt, I hope this serves as yet another voice in the crowd.
Whew….
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