Pond Salt: How much should you be adding to your koi pond?

A few common questions among pond keepers are, ‘Why should I use salt in my koi pond and how much should I add’? If used in correct doses, pond salt can offer many benefits to koi carp and pond water.

Before there was an extensive range of pond treatments available on the aquatics market, pond salt was the go-to solution for killing parasites and protecting koi carp during the winter months. In winter, salt helped koi by replacing salt that the fish naturally produce themselves. When pond water gets colder, the fish’s metabolism slows down and their organs begin functioning less than they would in warmer water. Using a small amount of salt helps to replace the natural salt they would normally produce but are unable to due to the slower functioning – this would, in turn, make the winter time more bearable.

Where / When To Put Salt in Your Koi Pond:

As stated above, putting salt into your pond in winter is a good idea only if you do not have a pond heater. If you have a pond heater, this will be enough to keep your koi functioning, healthy and warm enough through the cold. When temperatures begin to rise in the spring, make sure to change out the salt water using a ‘little but often’ approach. This means you do not have to perform any large water changes, just slowly change out the salt over a few weeks.

At the end of the day, you must remember that koi carp are a freshwater species and therefore should not live in salt water continuously over time. If salt is always used then the effects will stop working. It would be like if we took paracetamol every day – eventually we would become resistant and the effects would cease.  

An exception to this would be if you have a quarantine facility with a heater. In this case, using some salt can still be a good idea because it is a temporary tank set-up and can play a role in increasing the fish's natural disease resistance.

If you are using pond salt to treat parasites, add the appropriate dosage of salt (keep reading for dosing instructions below) and keep in the water for 2 weeks. After 2 weeks has passed, begin changing out your pond water to reduce the salt levels. Continue to change the water until there is no salt left. Again, if pond salt is used continuously, parasites will build a resistance to tonic salt and other pond water treatments will be required.

Types of Salt and Appropriate Dosing Levels:

A good salt to use is a tonic salt that contains no harmful additives and will be safe with fish, plants and filtration bacteria. Tonic salt is used because if its therapeutic and restorative effects. 

The dosage of pond salt is extremely important. It is recommended that 1 gram of salt is used per litre of water. It is also a good idea to space this out over time; using the ‘little but often’ approach again is probably best. Space out your salt treatment over the span of 3-4 days. Some people treat their whole pond at once but it is recommended that if you choose to do so, this is only carried out one time. Do not use treatment for the entire capacity of your pond more than one time. Just like any living organism, too much salt at one time can be deadly.

It is also important to let the salt dissolve in a bucket of the pond water before adding it to your pond. If this is not done, salt residue can build up on the bottom of your pond and can come in direct contact with your koi fish which can cause burns.

Pond Salt and Pond Plants:

While pond salt can aid in getting rid of and controlling pesky algae and blanketweed, certain aquatic plants are sensitive to salt. It is important to monitor salinity levels with a salinity meter so that you avoid pond plant mortality. To make it a bit easier, here is a list a few different pond plants and the levels of salt that they can tolerate:

If salinity levels reach 0.10% or above - anacharis, water hyacinths and lotus will not be able to live in the water.

If salinity levels reach 0.20% or above - lavender musk and water lilies will not be able to live in the water.

If salinity levels reach 0.30% or above – the majority of other aquatic plants will suffer. This includes forget-me-nots, zebra rush, cattails and floating hearts.

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