To counteract the effects of stress

A freshwater fish maintains an internal salt level of 0.9%, a level which is just under a third of the level of sea water (3.5%). Freshwater fish need salt, and if they don’t hold their body fluids at this level they will die. They use between 10-15% of their energy levels extracting salt from their environment and maintaining the level in their body at 0.9%. This work is carried out by their gills and their kidney. To explain this simply, their gills uptake salt, and their kidney reabsorbs most of the salt from their urine and excretes excess water.

When a fish experiences acute stress, their body releases hormones and neurotransmitters that make the fish breath faster, over-hydrate and lose salt. This can lead to an osmotic imbalance, the most life-threatening impact of stress. Stress factors include transport, parasite infection, bad water quality, handling, injury or spawning. There are many different signs of stress, and these include jumping, swimming erratically, laying on the bottom, floating on the surface, flashing, gasping, redness of the skin and excess mucus.

If a Koi is stressed, adding salt to the pond will divert energy levels used to uptake salt to other vital roles such as their immune response. Scientific studies have proven that exposing fish to a salt level between 0.25% and 0.75% reduces the negative stress parameters on a freshwater fish (1).

As a result of our hands on experience on the farm over the past 35+ years, and published scientific literature, we recommend that if a fish has been through a stressful situation, you raise the salt level to 0.75% to greatly improve its chances of recovering. This level should be held for 1 week, before slowly reducing the level with your regular weekly 10-20% water changes.

To help a Koi settle into its new environment

We advise that any Koi purchased from us that are under a year old, as a precautionary measure, are moved into a pond or tank containing salt. This includes our ‘Koi Fry’ and ‘Small Koi’ mixes. There is no harm in salting the pond when introducing fish over 1 year old, as this will also benefit them too. However, we find it more essential for younger fish. Young Koi have an immature, weak immune system (just like any young animal), and as a result often find it harder adapting to a new environment than older Koi.

To counteract the impact of transport stress, we recommend you raise the salt level in the pond to 0.75%. This level should be held for 1 week, before being slowly reduced by your regularly weekly water changes.

To counteract the effects of high Nitrite

Your biological filter works hard to keep your pond water safe for your Koi, and it does this by housing nitrifying bacteria. These bacteria break down harmful water parameters, ammonia and nitrite, in your pond water through the nitrogen cycle. To explain this simply, the bacteria convert the harmful waste your Koi produce into a much less harmful end product,nitrate. Without these nitrifying bacteria, your pond will quickly turn toxic, and your Koi will die.

Nitrite fixes to the red blood cells in the fish and subsequently reduces oxygen uptake in the gills. Nitrite poisoning is also known as Brown Blood Disease, or Anoxia. The more nitrite in the water, the less oxygen the fish can uptake, and as a result the fish slowly suffocates.

We find that moving additional fish into an existing pond often results in a nitrite spike. This is because the new fish are raising the biological load in the pond and the existing filter bacteria can’t keep up. Over time, the bacteria will multiply to consume this new higher load, but in the meantime the chances of a nitrite spike occurring are increased.

Just as people living at high altitude become accustomed to low oxygen levels, fish can become accustomed to high levels of nitrite over time. This is why existing fish may not show signs of stress from high nitrite, but newly added fish will. When a new fish is added into a pond that has an existing level of high nitrite, it won’t be able to access the oxygen it needs and will show signs of stress. For a Koi, moving into a new environment is stressful enough as it is, but when you factor in a high level of nitrite, you have a dangerous combination.

Signs you may have a high nitrite level in your pond include the Koi flashing, acting lethargically, listlessness, gasping at the surface, or “hanging” in the water.

Adding salt to the pond prevents the nitrite molecules from fixing to the red blood cells in the Koi, allowing more oxygen through, thus counteracting the effects of high nitrite. If your Koi are experiencing the effects of high nitrite in your pond, we would recommend you raise the salt level in the pond to 0.75%. This should be held for 1 week, before being slowly reduced by your regularly weekly water changes.

You can read more about nitrite in our article: https://cuttlebrookkoifarm.co.uk/pages/understanding-nitrite

To treat the symptoms of Carp Edema Virus (CEV)

CEV, also known as Koi Sleepy Disease or sleeping sickness, if left untreated, can be fatal to Koi. The virus was first reported in the regions of Niigata and Hiroshima in Japan in 1974 and has since spread around the world. Koi become very lethargic, unresponsive and will slip into a coma and eventually die. It has become common practice among many Japanese breeders to deliberately expose their young Koi to the virus by mixing them with older Koi, which themselves have already been exposed to it but have recovered – becoming carriers. As signs appear, the exposed Koi are treated by adding salt to their environment at a concentration of 0.5% - 0.75%. This is the only treatment that reduces the effects of the virus and allows the Koi a better chance to recover.

If you suspect your Koi have CEV (and you have already ruled out parasite or water quality issues), we recommend you raise the salt level to 0.75% for 2 weeks, before slowly reducing the level with regular 10-20% water changes.

Unlike the Japanese Koi breeders, we do not expose our Koi to the virus, as this would compromise our high level of biosecurity on the farm. As a result, a Koi purchased from us that is added to a pond with Japanese Koi may subsequently catch CEV.

To treat parasites

Costia

Formalin and Malachite Green (FMG) can be used to treat Costia (follow the instructions on the bottle). This treatment must not be used at temperatures below 12.5c. When water temperatures are below this level, salt can be used to eradicate Costia. We recommend using a salt level of 0.9% and maintaining that for one week before slowly removing with regular 10-20% water changes. Salt is also safe to use with Sturgeon, unlike FMG.

White spot

White spot can be treated with Formalin and Malachite Green (follow the instructions on the bottle). This treatment must not be used at temperatures below 12.5c. When water temperatures are below this level, salt can be used to eradicate White Spot. We recommend using salt at a concentration of 0.75% in the pond and maintaining it at that level continuously for six weeks before reducing slowly with weekly water changes. Salt is also safe to use with Sturgeon to treat white spot, unlike FMG.

Part of the life cycle of White Spot includes a cyst, and this cyst cannot be killed by any chemical treatment. Holding the salt level at 0.75% for 6 weeks will kill any juvenile white spot as soon as they hatch from the cyst. We have found this method far more effective in breaking the life cycle of white spot, rather than multiple FMG treatments.

Many years of experience have taught us that using salt is the most effective way to irradicate Costia and White Spot.

Salt Dips

A salt dip is where you remove a fish from its environment and place it in a small body of water (such as viewing bowl) and expose it to a very high concentration of salt. This practice is highly stressful for a fish and is not something we advise. Whilst dipping may kill a parasite on the fish, it doesn’t protect the fish against re-infestation once returned to the pond as the parasites will still be present in the water.

We do not recommend the use of short term, high concentration salt dips, under any circumstances, and believe that salt should only be used at a safe level in the pond itself. We do not recommend you expose your Koi to salt levels over 0.92%.

General guidance on the use of salt

Unlike other chemicals, salt is not removed through biodegradation, evaporation or oxidisation and can only be removed with water changes. Salt is a natural product Koi need a level of to survive.

Salt, when added to the pond, must be carefully sprinkled into the water, or first dissolved in a bucket of water. Any piles of salt not dissolved can cause chemical burns on fish that lay in or near it. If used in a quarantine pond or a pond of sick, sulking fish, extra care must be taken to ensure the salt is properly dissolved. Sprinkle the salt into the pond slowly, to ensure that there aren’t any piles of salt sitting on the pond floor.

We do not recommend the use of salt continuously in a pond. A healthy Koi does not need additional salt in its environment, it is perfectly adapted to living in a very low salt environment. To maintain a higher level of salt in a pond will not provide any benefit to a healthy Koi but it may provide an opportunity for parasites to develop an immunity to the effects of salt making it ineffective when it’s really needed.