Salt in Koi Ponds

Firstly, before I get into this topic I would like to make a disclaimer. When considering using salt it is always best to speak to a dealer about what you are doing first, there is a fine line between gaining good results and losing your whole collection of koi. Do not use salt without properly calculating your pond volume or without a salinity tester.

Quite often do I see hobbyists on social media questioning whether to use salt in their koi ponds, and I quickly realised how much of a conflicting topic salting your koi pond can be. I commonly see people referencing salt baths and salt dips too, again a very dangerous game if done incorrectly. A salt meter is an absolute must for any koi keeper considering putting salt anywhere near their fish. This will help you gauge how much salt is in the tank/vat if doing a dip or the salinity level in the pond if adding salt to the whole system. 

Dips in very high concentrations of salt are hugely stressful for a fish.  Whilst dipping may kill a parasite on the fish, it doesn’t protect the fish against re-infestation once returned to the pond, and it doesn’t address the cause of the problem.

A freshwater fish’s blood has a higher concentration of salt than the surrounding water – 0.9% to be exact.  Freshwater fish need salt – without it they would die.  10-15% of their energy from food is spent extracting salt from the water they are swimming in and then not losing it. If they are struggling with a health issue, adding salt to their pond will mean that can divert that energy to supporting their immune system when it’s needed most. 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.

Salt itself can be a great tonic for fish, as it increases osmosis rates for koi and allows them get oxygen into their bloodstream more efficiently, therefore reducing stress. It also hinders the osmosis process for some parasites and aids in killing them off. However, salt shouldn’t be just thrown into your koi pond, and definitely not without identifying what’s going off. Most dealers use salt in their quarantine process when bringing fish in to help the stress levels after long journeys that the fish may have been subject to. It is also used by dealers or importers when bringing fish from Japan as the breeders tend to maintain a salt level in the pond before shipping to allow the fish to be as calm as possible.

The downsides to using salt include the inability to use certain treatments with salt present in the water, and also the length of time it takes to flush from the system. Even with a trickle in system running on the pond, it can take months for the salt to be completely washed out of the system. For example, should you treat the pond with salt for any reason, and then come across an instance where you would require a treatment of potassium permanganate, the treatment cannot be done until the salt levels are extremely low. A dose of 0.6% ppt is a good level to treat fish, but will take a long time to get this out of the system, anything less and you’re just aiding the osmosis of the fish, rather than actually addressing any parasite issues. 

A healthy Koi does not need additional salt in it’s environment.  It is perfectly adapted to living in a very low salt environment. To maintain a higher than normal level of salt in a pond artificially 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.