A few things from the experts that you need to read and understand if you have a pond with koi and are thinking about using salt.
1. SALT: THE BASICS
The use of salt for either prevention and/or maintenance depends on what you are trying to accomplish. Let's look at a couple of salt corollaries and for practical purposes, "salt" and "chloride levels" are used interchangeably. I mention this because many folks use calcium chloride to raise their GH levels (a good thing) and this contributes to the overall pond water "salt" level.
1. Natural fresh water has a salt (chloride, actually) level ranging from .02 to .1% depending on where you live and your source water. City water tends to have lower chloride levels than well water. So, you can pick any number inside that range for your "normal" salt range. Most folks do not add extra salt for normal operations and just rely on the "natural" levels and this is absolutely fine.
2. Higher levels of salt, let's say in the .15% to .3%, can be used for long term medicinal purposes. Mostly we use salt in the .15% - .2% range to fend off nitrite uptake when the filters are maturing and nitrites are present. You can keep salt in this range for as long as you need to, although the plants may object some.
3. We use salt at .3% or so for stress relieve. The added chloride levels in the water make it easier for the fish to process water across the gills (reduces osmotic tension/pressure on the gill cells). Normally we recommend .3% for fish in stress from moving, sickness of any kinds, etc. You can keep this level of salt in the water for as long as you need it (the key word being "need.)
4. Salt levels above .3% and not to exceed .6% are used for baths when we suspect parasites (other than flukes and lernea/anchor worms). This is short term exposure, usually no more than 30 minutes. Salt baths are good for fish with suspect environmental dropsy where the osmotic process has gone awry and needs to be kick-started.
5. Some folks recommend using salt levels over .6% for parasite eradication... I am not one of them and .6% is my limit. At .9%, the chloride level in the water equals the chloride level in the fish's blood and the osmotic process balances, but physiologically, the fish is being stressed by the higher levels of salt. Above .9%, we stand the risk of reversing the osmotic process and in doing so, really causing physiological problems with the fish. I never thought that was a good idea under any circumstances and that there are better ways to fight parasites than .9% or higher salt levels. Arguably all chems are stressful to the fish to some extent and once we understand that, we can select the best protocol for the problem at hand.
6. Once upon a time we believed two things to be true: 1) Salt killed most parasites and 2) higher levels of salt in the pond during winter/cold water times were good to fend off parasite attacks. We now know neither of these are true statements. The overuse of salt by everyone (but mostly the breeders) has created salt-resistant parasites and while we can still do some damage to most parasites with the right salt levels, there are better and more efficient and sometimes less stressful ways of battling parasites. Whether you have salt-resistant parasites can only be determined by trial and error and using a good scope. I have not seen any salt-resistant parasites personally but we cannot deny that they probably exist.
High levels of salt in the water over winter we now is not only dumb but dangerous to the fish. And here we are talking about levels above "natural" levels. We know that increased levels of salt in the water changes the physics of the water by reducing the water temperature where water becomes its most dense and this is bad for the fish "under the ice." So, no high levels of salt in cold water...period.
2. SALT: ITS USES
Salt has been used on such a large scale and usually for no reason that most parasites are resistant to it. There are exceptions:
Salt is known to protect fish from nitrites. The percentage of salt is kept at .15%-notice decimal point.
Salt is required at .6%, at least so the story goes, when using Elbagin (a Japanese water column antibacterial agent very similar to Furazone Green).
Salt will aid osmotic regulation of an immuno-depressed fish. New imports as well as fish with bacterial infections are sometimes treated to aid their recovery. However this practice is no longer so widespread as it has become recognized that the overuse of any medication leads to resistance and diminished effect.
Two parasites can still be controlled with salt. They are Chilodonella and Ich. The percentage of salt in this case is .6% and the duration of treatment should be 14 days. Most other parasites are not deterred by salt.
A salt dip has it's place in this hobby. Setting up a .9% dip as a parasite treatment works fairly well when the parasites are heavily infested and no other medication is readily available. Place the fish in the dip until it rolls over. Then remove it to fresh aerated water. Do not leave the fish unattended during this procedure.
Salt occurs naturally in most waters. It is unnecessary to add it to pond water as a constant treatment. In fact doing so will further reduce the effectiveness of salt when it is actually needed. Here is how to calculate salt:
.1% salt in 100 gallons is .8333 pounds.
.3% salt in 100 gallons is 2.5 pounds.
.6% salt in 100 gallons is 5.0 pounds.
.15% salt in one US ton(264) gallons is 3.313 pounds.
Source: Karl Schoeler
3. SALTING THE POND OVERWINTER:
Just recently, I got a newsletter from a pond equipment retailer (of excellent reputation BTW), that discussed wintering over the pond. I can imagine the great number of people that this went to, including some KoiVet members that are now scratching their heads. Because we could possibly violate copyright protections, I won't print what the newsletter said but it mentioned that salt at levels of .3% offered added protection to the fish via an increased slime coat, and that .6% salt levels kill off nearly all of the parasites, bad bacteria, and fungus in the pond.
All of this goes against conventional wisdom on the issues of salt and cold water. We know this here.
From REC's KHA Continuing Education "Cold Water Koi Keeping" paper:
It is important to point the affect of salinity levels on water temperature. We know from physics that fresh water under standard pressure and within bounds of natural salinity levels (.02 to .1 %) reaches maximum density at about 39 deg F. Ostensibly this means that a pond of proper depth and volume for a particular area of the country will not achieve water temperatures below 39 deg F at depth. We also know from physics that if we increase the salinity levels of the water, we lower the temperature at which water reaches its maximum density. This is why ice cream is made with salt and why salt water does not freeze at 32 deg F like fresh water. As temperate fish, koi will withstand water temperature down to 35 deg F before being affected by hypothermia and given this thin line of maximum water density (39 deg F) to the lower limit of35 deg F, we can see that allowing an elevated salinity level (>.1 %) has the potential to cause serious problems with the fish's well-being. This fact needs to be considered when applying salt in cold water conditions whether to prevent nitrite poisoning or parasite control.
4. SALT AND THE SLIME COAT
Q: I thought that you want fish to have a good slime coat and isn't this the main reason to add salt when needed?
A: This is a long winded one- sorry but the big picture needs to be addressed first.
Dogs shed, snakes peel and even people have flakes of all sorts! Fish have two stories to their shedding! First, like all animals, koi shed their epithelial cells and, in their case, their mucous layers. This is the normal life cycle of the mucous and epidermis and the process of exfoliation.
Secondly, fish use these mucous layers to trap and shed all those things that wish to permanently live on their outer body surface. So as a fish swims, the slime coat’s microscopic surface is moving outward, backwards and off the koi. This becomes part of the ever growing organic content of the water column. And within it are trapped parasites, bacteria, dead white cells, color cells and epidermal cells - all exfoliated over time.
Along with this dynamic is mucous layer’s other purpose- to act as a protective capsule for keeping fluids in and offending inorganic molecules out of the skin layers. This creation of a less- than-semi-permeable condition helps koi to resist chemical pollutants and heavy mineral effects of certain water types. These are the realities of many of our closed systems. And the reason koi can manage in such a system is very much dependent on slime coat function.
But as amazingly complex as koi are, they are also primitive in design. And the ability to generate massive amounts of mucous in response to outside insults is ultimately limited. This is a form of physiological exhaustion and often seen in ponds with huge DOC content, over medication, very hard water and very high/low pH water. Things like shimmies and buff colored skin are later indications of such an environment.
. . . . . and
Back on topic- yes chemotherapy does affect host and parasite most of the time, often in subtle ways. Certainly the environment is almost always effected which in turn, acts in other ways on koi. So the reduction of slime coat can be:
1) the effect of the chemical itself- that includes the water parameters that the chemical reacts with- hardness of water , pH and temperature for example.
2) the secondary effect of the chemical has on the water quality which in turn effects things like slime coat in a series of cascading changes within the pond and its microbial life/stability.
3) a possible negative synergy produced by two compounds in the water- not necessarily limited to those things consciously added by the keeper. Sodium chloride (salt) levels for instance are first an irritant and then an astringent, creating a powerful synergy of demand for over-production plus a drying out of the coat itself.
In all cases you can interpret the results of a limited or missing slime coat as either a koi living in an environment that slowly eroded away the coat or by the immediate exhaustion of that slime coat production by some chemical/organism introduced to the pond.
. . . and
That is the slime koi in theory! In our ponds however, the slime coat faces challenges that nature never intended. Contact with koi nets, koi socks, chlorine, human hands, flashing on plastic pipe edges and concrete walls, and erosion- from poor water, heavily laden ammonia, nitrite and nitrate water, salts and chemicals. The slime coat is renewable- but at a limited rate of replacement. And it creates the illusion of being durable and omni-present until mucus cells cease producing.
. . . and
The [whitish] film/patches you see on your koi in winter are one of two things: Costia or, more likely, excess dead mucous coat. This is very common in winter and can be resolved with warm water and aeration. Ironically, it is the salt that assists in causing this build up as it first stimulates the mucous cells to work over time and then dries out the thickened mucous.
Normally koi swim, no correct that, ‘slide’ through the water. The mucous is worked backwards by this friction and leaves the body into the water column. This is a form of grooming for the koi but also serves the important function of casting off would-be foreign invaders. Finally, metabolites of the dermis and epidermis are lost through this action.
When a koi is in stasis, the normal slime removal is stopped. It is not unusual for it to become caked and ‘dead’ on the resting fish. Interestingly, these white patches always seems to be bilateral on the head (in crevices and creases of the skull and gill plate), a patch on crown or nose and along the body in islands.
When you warm fish up, you THEN can add some salt to stimulate normal slime production and encourage the sloughing of the old patches.
You might also notice that koi will blow bubbles over and out of the gills during this time. That is slime production caked on the lamella that they are grooming off.
Again, to an inexperienced eye, it is best to scrape this patch and make sure it is slime and epithelial cells and NOT costia or chilo.
Salt can be a wonderful tonic and mild form of chemotherapy or it can be badly misused. And it can also cause 'resistance'. Worst yet, koi exposed to salt for too long a period will adapt to it. But not before salt turns from an irritant (that is how salt works in increasing the slime coat - it irritates the mucous cells) to an astringent. As an , salt dries and cracks slime coat. And eventually it has the opposite effect- it thins the slime coat. Unfortunately this is another example of a ‘good thing’ being over used to the point of being counter productive.
Salt’s greatest power lies in its ability to cause osmotic change - quickly. This is why it is best to hold off on salt until you actually need it. The more you use it, the less effect it will have. The less you use it, the more dramatic the effect will be.
In winter, a koi’s metabolic rate slows to a fraction of what it is in high summer. The koi shuts down to conserve energy and lives mostly off of glycogen reserves stored in the kidney, liver, brain and muscles. Salt is not contributing much, if anything, to the situation in this state, as even slime coat production is slowed. In fact, the congestion of slime coat on the gills is best avoided in stasis. And the cool water parasites present are simply adapting to brackish conditions in such a setting.
Almost all spring problems are the result of winter stress. This stress is temperature related. If one is interested in getting to the actual cause of stress in winter than HEAT, not salt, is what will help. Instead of testing survival rates at nature’s culling temperatures, it is probably wiser to encourage seasonal hormonal cycles with shorter and less demanding simulated winter conditions (water in the mid to high 40 degree F range at most and for 12 weeks at most).
5. SALT: WATER DENSITY & TEMPERATURE
Salt is almost useless against sap except at VERY high dose rates...somewhere in the .6% or higher level. And this is absolutely not practical in cold water except as a dip. As Lee mentioned, an increase in salt levels (let's say anything over .1%) lowers the temperature at which water becomes its densest. Under normal fresh water conditions, water is most dense at 39 deg F and this is the level our fish have adapted to. By increasing the salt level, the temperature lowers beyond the point our fish can tolerate it and bad things happen. So, for now salt is out of the question.
6. SALT: STRESS & OSMOREGULATION
Koi are born into a watery world that offers quite the predicament - how to get the needed resources from the surrounding water WITHOUT becoming exactly the same as the surrounding water chemistry? Thankfully, evolution has created the perfect answer! A koi is protected from its greater environment by skin and scales and is pretty ‘water tight’.
But then the original problem, how to get good things in and bad things out? For this, the koi has gills and the lining of the gut. And so, the gills act as both ‘lungs and kidneys’ in this role of exchange with the outside world. At the level of the gill, the exchange of molecules takes place on constant and routine basis as the fish strives to maintain what is known as homeostasis. And any disruption to homeostasis puts a koi in a world of imbalance and is usually at the heart of all causes of death in koi.
Within the base of the gill filament are normal epithelial cells and also specialized cells (chloride cells) that use both osmotic pressure principles and electrochemical gradients to ‘exchange’ toxic ammonia for much needed ions. So while the gills epithelial cells passively loose Na+ and CL- to the realities of passive diffusion, these negatively charged specialized chloride cells along with an ATP ion pump, are discarding some things like H+ but ‘recapturing’ other things like Na+ and CL (as an exchange with NH+4).
The result, in normal operation, is that a koi maintains a zero loss in salts. So in the koi’s battle to maintain 300 mOsmol/L (pressure) in its blood, despite the osmotic tendency to gain water and lose valuable ions, our koi actively search out ions from the environment while all the time excreting water from its body. So when all systems are firing, a koi wins by preventing salt outflow at the gills, and on the other end, by producing a huge amount of dilute urine after the kidney captures additional salts. This, by the way, is why koi never drink, as they gain the water they need constantly from the gills which is in effect ‘a screen door on a submarine’.
But when a koi is transported, several things happen that interrupt this normal homeostasis. First the koi, as mentioned earlier has ‘this train’ of toxic gases and nitrogen waste products eventually stopped as the bag ‘fills’ with enough byproduct ions that no more can passively leave the fishes blood at the level of the gill.
Number two, the gills themselves become congested with mucous and red blood cells further blocking the ease of ammonia to leave and sodium to enter. And these concentrations of ammonia in the plastic bag, at levels of 10-12 mg/l, will cause telangectasis of the gill lamellae (basically swelling of the blood vessels) resulting in further difficulties maintaining homeostasis.
And thirdly, as I mentioned in a previous post, the GAS or general adaptation syndrome, is a fight or flight response that pours large amounts of adrenaline and cortisol into the blood stream. This is great stimulus for ‘escaping’ and surviving short term challenges but it is a huge trade off to normal metabolic function. Things like a decrease in plasma osmotic pressure results from a loss of ions over the gill as all energy is diverted to muscle. And since a koi has that normal gradient relationship with ‘outside fluids’, during stress, the normal 130 mOsmol/L of chloride in the blood will decline continually while in the bag, to almost half (called hemodilution). This of course, results in additional, and sometimes, massive physiological disruption.
Now where does salt come in, in all of this?
Simply put, it ‘helps’ by lowering the osmotic gradient between blood and water thus slowing hemodilution. It does NOT stop or reduce the root cause of our problem -namely, GAS. It is important to realize that the general recommendation of salt use levels was introduced when science only knew of diffusion and osmotic models/dynamics in freshwater fish. That is to say, they did not consider the active role of electrochemical dynamics and active scavenging of sodium and chloride. So the context and bigger picture was lost in the logical, albeit simplistic, model of hemodilution. So providing some presence of Na+ and CL- can be helpful (but maybe not as it was interpreted even ten years ago).
The issue of the amount to use will always be argued as the koi seem to benefit at most reasonable doses. But logically, if we know that salt is also an irritant, we do not want to irritant/ stimulate swollen gills already congested with mucous and red blood cells right out of the bag.
As I mentioned, salt is many things- the thing that determines which effect it will have is strictly down to dose and exposure time - a mild tonic, an irritant, an astringent, an osmotic disruption, a chemotherapy, a parasitic agent– it is all about dose and exposure. And at the extreme ends of these parameters of dose and exposure time are extreme differences and even opposite effects.
For example: Do we want to use such an amount (dip strength) that is a known killer of protozoa but is also a known osmotic disruptor of fish homeostasis at a time when koi are in need of homeostasis?? The obvious answer is of course not. So we attempt to thread this needle by monitoring exposure time. Wrong headed. In a breeder setting, this is a trade off. In a home setting, we treat to the need based on a diagnosis, no more and no less.
The logic is pretty simple once you have the information. Add .1 or .2% to help equalize the gradient between a koi’s ‘outside world’ fluid and it’s ‘inside personal fluid’. Forget about of the old idea that sodium and chloride must be in massive amounts to restore salt balances inside the fish - at .1%-.2%, there is more than enough Na+ and CL- to operate and stabilize the fish. And in the first step if quarantine, this is all we are looking to do. Koi are not brackish water fish.
This is getting really long, but some other time we can talk about the next level of need for salt- in a fish that is actually sick.
Hope all of this helps. Questions, comments and concerns welcome.