This article was first written for and published by Koi Magazine in 2009 (edited 2017)
At Cuttlebrook Koi Farm we use salt only when we have to but there can be a number of reasons for doing so. When Koi are being grown in the mud ponds they live in a soup of natural salts – this is their natural environment where they flourish and have evolved to live. When we harvest them from the mud ponds and transfer them to the concrete or re-circulation ponds we must add salt to the indoor systems. If we don’t do this the sudden change in salt levels causes the Koi to suffer an osmoregulatory imbalance that causes a kind of “sleeping” sickness. The dose rate at this point is 0.6% (6kg per cubic metre (220 gallons)) although with most fish we take it up to 0.75% (7.5 kg per metre cubed). At 0.75% the salt does two jobs, it helps with the osmotic imbalance caused by moving from a mud pond to clear water, and it clears the fish of any ecto parasites * (apart from flukes which it suppresses but doesn’t eradicate). So, salt at this level can also act as a medication. The Koi’s own natural body salt content is 0.9% and whilst they are designed to cope with a natural ingress of water, higher salt levels than this should be avoided. (Interestingly, some Koi farms in Europe and Israel have been known to grow Koi in brackish water, so it has been shown that Koi can tolerate quite high concentrations of salt.) 0.3% is what I would call tonic level. If a Koi has gone through a period of high stress, then salt at this level can calm the fish down. It also stimulates the production of mucus – the Koi’s external immune system. 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 and, at slightly higher doses, have evolved to tolerate.
I don’t believe in salt dips as I believe that they are hugely stressful to the fish and can strip the mucus layer. Whilst dipping can kill any parasite on the fish, by stripping the mucus layer, it can leave the fish defenceless against re-infestation once returned to the pond.
Salt, when added to the pond must be dissolved first as 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, care must be taken to ensure the salt is properly dissolved.
*Update August 2017: We have recently found that some Costia can only be eradicated with salt at 0.9%, held at that level for 3 days.
Laws of using salt
Don’t use it unless you have to.
- Only use it as a medication.
- Always dissolve it first when you add it to your pond.
- Try to bring the salt levels down again as quickly as possible (to 0.02% – 0.05%) once the fish have recovered.
- If you are using salt, you must have a salt meter. You can’t dose properly without one. If not a salt meter, then a hydrometer.
- If you don’t have a meter, calculate the pond volume in meters cubed at 1kg per meter cubed to 0.1% salt concentration. Therefore, 30kg of salt is added to 10 metres cubed (2200 gallons) for 0.3% salt.
- Don’t use any other medication with salt apart from those recommended by the manufacturer as being safe to do so. (Especially DO NOT use with Formaldehyde (Formalin))
- Only use cooking salt or PDV (Pure Dried Dacuum). Other types of salt can contain iodine or anti caking agents which could be harmful to the fish.