Wait. Add salt to a freshwater pond? Why would I do that?
There are many benefits to our freshwater fish by increasing the salinity of the water. So let’s look at those 3 main questions; What, Why, and How Much.
What. Salt. Yep, regular old sodium chloride...NaCl. But the key here is that you want PURE salt. No additives at all. Common additives to salt will be iodine and yellow prusisate of soda. These should be avoided. Only pure salt.
Why. Salt has many benefits to our pond fish, acting as both a treatment and preventative.
- Adds electrolytes.
Improves gill function
Stimulates natural fish slime coating
Improves defense to disease, nitrite toxicity, and general stress.
Safe fish and the surrounding environment.
Does not harm biological filtration.
Can kill many parasites
How Much. The dosage amount for pond salt will vary depending on the purpose and details of the application in which it is being used.
Anything over a 0.1% salinity can be harmful to plant life. So if adding salt as a general tonic you will want to keep the salt level under 0.1%.
A 0.1% concentration is achieved by adding 0.8 pounds of pond salt for every 100 gallons of pond water.
If you are adding salt to kill parasites or if you currently have fish dying then you will usually shoot for a 0.3 - 0.5% concentration. Again, this level will harm most plants. This concentration will be achieved with 2.4 - 4.0 pounds per 100 gallons.
Salt Baths. Another option when you have a sick fish that needs an individualized treatment is a salt bath. Prepare the bath using pond water and add about 1 pound of salt per 10 gallons. Allow the fish to sit in the bath for 5-10 minutes then return to the pond.
Other notes on using pond salt. Due to the issue of higher salt levels harming plants in the pond one approach it to increase the salinity to the 0.3 - 0.5% concentration for the cold months. Spring is usually the most stressful time for our koi and goldfish. Adding a higher dosage of salt in the fall after plants have been removed or gone dormant can help get your fish to a healthier start in the spring. Just remember to dilute the salt prior to the time your plants begin to grow.
Salt does not dissipate or evaporate. Once it is there, it stays until the salinated water is removed either through overflow or a water change. As such you may need to test the salt level to ensure the salinity is where you want it to be.