When and How To Use Salt

When and How To Use Salt

At Cuttlebrook Koi Farm we use salt only when we have to but there can be a number of reasons for doing so. 

When we harvest our Koi from the mud ponds and transfer them to the concrete or re-circulation ponds it’s a stressful time for them. When a fish experiences acute stress from injury, disease, handling or transport, their body releases hormones and neurotransmitters that make the fish breath faster, over-hydrate and lose salt.  This can lead to an osmotic imbalance as a result of ion depletion – the most life-threatening impact of stress.  To counteract this, we add salt to their tank  to a level of 0.75% and maintain it at that level for one week before reducing the level gradually with our regular water changes.

 At 0.75% the salt does two jobs, it helps with the osmotic imbalance and it clears the fish of some parasites (apart from flukes which it suppresses but doesn’t eradicate and Costia which requires a higher concentration).  So, salt at this level can also act as a medication. Salt also stimulates the production of mucus – the Koi’s external immune system. 

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.

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.

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.

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.

*Updated May 2020

You will find a salt calculator in our pond calculators article.

Laws of using salt

Don’t use it unless you have to.

  1. Only use it as a medication.
  2. Always dissolve it first when you add it to your pond.
  3. Try to bring the salt levels down again as quickly as possible (to 0.02% – 0.05%) once the fish have recovered.
  4. 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.
  5. If you don’t have a meter, calculate the pond volume in metres cubed at 1kg per metre cubed to 0.1% salt concentration.  Therefore, 30kg of salt is added to 10 metres cubed (2200 gallons) for 0.3% salt.
  6. 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))
  7. Only use cooking salt or PDV (Pure Dried Vacuum).  Other types of salt can contain iodine or anti caking agents which could be harmful to the fish.