Salt In Freshwater Aquariums - The In-Salting Truth
Using salt in the freshwater aquarium has long been a staple remedy of many enthusiasts within the freshwater trade. Got fungus? Ahhh, throw in a bit of salt. White Spot? A bit of salt will get rid of that. Columnaris? Itching? Lethargy? A bad hair day? Throw in a bit of salt, mate. She’ll be right! Right?..... Wrong!
It never ceases to amaze me how this apparent ‘wonder drug’ can be utilized in such a haphazard fashion with seemingly little to no regard for the type and size of fish being treated, the type of disease it is administered for, and the contributing external environmental factors involved. All of which need to be considered very carefully before diagnosing and implementing ANY treatment regime, however time and time again an arbitrary measurement is delivered to an unsuspecting aquarist with little to no prior knowledge of fish physiology and medicine from an aquarist who has been ‘doing it for 30 years, mate’, and lacks the exact aforementioned knowledge in worryingly similar amounts.
It should be a no-brainer that not all fish are the same. One of the most diverse families of animals on the planet, fish can come from every corner of the globe. From warm to cool water, from soft water to very hard water, high in mineral content such as calcium and magnesium. They come from the Amazon and the rift lakes in Africa. They come from Central and North America to South East Asia. They have all evolved differently over the millennia. So it would also stand to reason that their tolerance for certain elements (let’s choose salt this time) would also be quite different. Agreed? This makes it incredibly difficult to administer a correct dose based on the particular physiology of your fish without a far-reaching and very thorough understanding of your fish’s evolutionary progress and current salt tolerance and requirement. Yet… time and time again, a flippant and often irresponsible dose is spouted with little to no regard for these kinds of factors. Many of us keep South American fish, and many of these fish come from waters with a very low TDS (Total Dissolved Solids) level which is generally attributed to a low General Hardness reading but will also include a low level of Sodium Chloride. Many South East Asian fish and even Africans also come from waters similar to this. Now given that most of us have acclimatised our fish to tap water, or even in some cases tried to condition our water with the use of certain products available from the aquarium, and now coupled with the fact that our tap water is always alkaline, and will generally fall within a General Hardness range of between moderately hard to hard, it is baffling to me how so many aquarists out there can continue to move the salinity level of their aquarium even FURTHER outside the range to that which their prized fish have so carefully been acclimated to over millions of years. That is… a low salinity level and expect their fish to just ‘cop it on the chin’ coz it is ‘good for disease’. What a crock!!
As a general preventative salt is generally thought to induce an extra ‘slime’ layer on the fish, thereby helping to protect it against various parasites. This can be thought of as true. The downside to this is that fish induce slime on the outside of their bodies through the use of specialised skin cells that can be induced to release slime through the release of a hormone or else when they become irritated. Now since we are pretty sure that salt does not contain said hormone, it can be deduced that salt induces slime by irritating the skin of your fish. Hardly seems like a stress reliever to me. Why don’t you pull out some nose hairs when your eyes get dry? That will make them water again right? It’s the same thing with fish.
Let’s move on to the actual efficacy of sodium chloride salt as a treatment or even a ‘cure’! As many aquarists will attest, salt is an essential part of a healthy aquarium, choosing to maintain a regular salt dose for the ‘benefit’ of their fish and the reduction of parasite infection. My first instinctive reaction to this is that if you are keeping your fish properly in water that is high quality then parasite control should be relatively easy for you anyway without having to rely on a ‘back-up’. As Dr. Robert. T Ricketts , a renowned scientist and lifelong aquarist, states “Brackish and estuarine fish are able to tolerate and likely to prefer more than only slightly higher Total Dissolved Salts, or osmolarity. In nature this is coupled with increased pH from the other salts dissolved in the water: calcium and magnesium carbonates and bicarbonates prominently. These materials "buffer" the water at higher pH levels than waters lacking these ions. So in the wild these fish arose in or frequented waters with ALL these ions and more. Adding salt, NaCl, alone will not affect the pH at all. Adding marine mix will provide a situation more like that from which the fish's forebears came. So long as the levels are below those that would register on a full range hygrometer, short-term exposure will do little harm (disease treatment), but long-term exposure should be reserved for fish with the physiology to live in that situation.”
Insofar as salt as a healing tool for wounds and lacerations goes, it is often thought that adding salt can help to ‘draw’ toxins and nasties back out through the skin of the fish through the use of osmosis, or the tendency for a less dense fluid to naturally follow the path of a more dense fluid. Let’s knock this one on the head quickly, as to increase the salinity of the surrounding environment of your fish as to be able to outcompete the salinity of it’s own blood, you would quite easily have a very dead fish on your hands… and a very salty one at that.
Further to this, some aquarists will claim that the osmotic ‘stress’ on your fish can be reduced by bringing the salinity of the surrounding water to more closely match that of the fishes body. Well, for this to be true, one needs to be able to ask the fish if he is feeling a little stressed, and if that stress is caused by fluids passing too aggressively through his (or her) body. If you receive an emphatic yes, then by all means… salt away. Laughable as this is, without a very thorough knowledge (again relating to thousands of individual fish species available in the trade today) of each one’s specific physiological requirements and adaptability, as well as the myriad other stimulus that may or may not be affecting your fishes ‘stress’ level, this is another dangerous game to play. Stress is a funny term, and can often not be quantified easily. What is stress? Why is your fish suffering from it? What is the effect it is having on your tank’s inhabitants? Surely adding a pinch of salt to reduce osmotic ‘pressure’ (and I put this one in quotation marks as well as it is a VERY loose term) is likely to do more harm than good (refer to my paragraph on where fish come from).
Adding salt will deliver electrolytes!! Sure it will. But do you know what electrolytes are? Well, basically any dissolved salts within your aquarium water can be classed as electrolytes. So which ones are you adding? And in what quantities? And does your fish really need them? Certainly your tap water contains electrolytes, something often overlooked by ‘experienced’ salt users. Minimal amounts of electrolytes are available through your normal water change regime and it is unnecessary to buffer this natural amount through the introduction of yet more salt which will also be performing other undesirable functions such as (as mentioned before) irritating the skin of your fish and helping to move it outside of it’s own normal comfort zone, from an evolutionary standpoint.
There are a few fish that will tolerate and even appreciate salt levels within the aquarium, however these fish are few and far between. They are classed as euryhaline fish and are the only group of fish that can quite happily tolerate various levels of salinity and even require it for reproduction. There are still other groups of fish, classed as anadromous (live in the sea but only come to fresh water to breed) and catadromous (live in fresh water but go out to sea to breed) while the vast majority of fish are classed as stenohaline, which means they have a very low capability to adapt to changing levels of salinity. So do your fish a favour in many more ways than one. Add salt only when you are ABSOLUTELY sure it requires it for normal biological function and not because you think it is ‘just good’ for your fish despite the claims you may hear.
The practice of not using salt within a freshwater aquarium is pretty heavily steeped in science and fact nowadays while the apparent ‘pros’ can be usually only be verified by ‘old man salty’ who has been ‘doing it for 30 years’ and can vouch for the 'scientific' merit behind salt and it’s Harry Potter like magical properties.
By Shane Matheson
References:
The Skeptical Aquarist
https://www.skepticalaquarist.com/salt-magic
https://www.skepticalaquarist.com/salt
https://www.theaquariumwiki.com/The_Salt_of_the_Earth