O Noes! More Salts!

Salt? Again? Do we use it or not, and if we do, what for? What we think about salt in our ponds changes as we talk to different experts in the field of aquaculture, and some of the finest arguments I’ve gotten into lately seem to have salt at their origins. There is no question that the versatile compound of a poisonous gas and a toxic and explosive metal has a place in the management of our ponds, and it is time once again to review its current place in our ponds.

A healthy koi does not need salt. Neither does a healthy pond. Koi are carp and carp are fresh-water fish. Their physiology allows them to pump free water out of their tissues back into their environment and maintain very much the same tissue concentrations of salt and water that all living creatures on this planet enjoy. To do this, they expend energy, and being cold-blooded and dependent on the water temperature around them to determine how fast their metabolism turns over, that energy budget is limited. That being said, salt has been shown to be helpful in the management of stressed and injured fish, presumably by lessening the osmotic difference between the inside of the fish and the outside environment, allowing the fish to clear more free water with less energy expenditure. This may allow more of the available energy to be devoted to the koi’s immune response to infection or parasitic infestation, or to devote to wound healing. Ulcers may also be helped with salt, since they represent a hole in the barrier between the inside and outside of the fish. A healthy koi uses its skin, scales and slime coat to keep free water out, and that protection is lost when an ulcer forms. Salt in the water reduces the free water diffusing through the ulcer and in turn reduces the amount of water the fish has to pump back out.

How much to use is open to argument, and you’ll get a different answer from every expert you talk to. The numbers you hear the most range from 0.15 to 0.3 per cent salt, with some advisors going as high as 0.6 per- cent in isolation tanks for very sick fish. Concentrations as high as 2 lb of salt in 10 gallons of water are frequently used as a dip to terminally discourage parasites.

An extensive online search on the subject proved interesting. Google Scholar yielded 133,000 articles incorporating pond and salt. None of them were in any way related to backyard koi ponds and most of them dealt with construction and maintenance of power-generation from non-convecting salt ponds. Narrowing down to keywords “Koi, salt” got me 22,000 articles, only one or two on subject. Those from actual scientists dealt mostly with using high-concentration salt baths as a dip or disinfectant. The only mentions of salt use in ponds fell into three categories. The first set dated from my last search about three years ago and centered around a series of articles by Brett Fogle, who runs MacArthur Water Gardens, an online commercial operation that sells (you guessed!) pond salt. He was all for constant and consistent use. Interestingly, newer articles and posts from him have changed their tone, and he’s a lot less enthusiastic about it now. The second set represented the majority opinion in the articles, posts and blogs that I sampled. Salt is useful as an anti-parasitic dip and an early spring treatment for protection against high nitrite levels. It is NOT recommended for constant treatment in the pond. The third set recommended avoidance of the chemical entirely, except as a high-concentration dip for transported fish, or fish fresh out of the mud pond, the sudden osmotic stress serving to explode most of the parasitic load on a fish on contact. It was interesting to note that the geographical locations of these sources were generally places that did not experience winter.

Salt’s ability to kill parasites is problematic. Epistylis, Trichodina and Ichyophthirius (Ich) will be inhibited (but not eradicated) at concentrations of 0.3% and this effect is often temporary. Fish with leeches, Anchor worms and Costia require individual dipping in 2% salt baths as well as 0.3% concentrations in the pond water, though repeated or extended exposure to salt tends to generate tolerance and resistance to treatment. Dactylogyrus and Gyrodactylus (gill and skin flukes) laugh at salt (a sniggering Dactylogyrus is a nasty thing indeed) and many of the effective treatments require low or zero salt concentrations to limit toxicity.

There is no question in anybody’s mind that salt is vital in early spring. As the populations of nitrifying bacteria wake up and start the conversion of ammonia to nitrite to nitrate, it rapidly becomes clear that the crew that handles ammonia-to-nitrite are the cheerful early risers, while the nitrite-to-nitrate gang seems to need several cups of strong coffee and a couple of extra weeks to get going. During that high-risk period, salt provides protective chloride ion to compete with the nitrite in the fish’s blood. The necessary 30:1 ratio of chloride to nitrite is easily supplied by a 0.2% salt concentration, maintained until nitrite levels drop to zero.

Frequent water changes and very limited feeding will help keep the problem under control.

Okay. If you are going to use salt, it is critically important that you know how to manage it. There are RULES.

Rule 1: Salt in your pond is there forever. If you have evaporative losses, the concentration goes up. The only way to get rid of it is to do water changes. Many, many water changes.

Rule 2: Salt kills plants. Sometimes this is a good thing. Salt in the pond in early spring can limit algae blooms, although it won’t eliminate them entirely. Concentrations higher than 0.2% will wipe out your tender aquatics and keep your water lilies from thriving. Watering your garden with salted pond water gets you the Sahara desert.

Rule 3: You must know how much salt you have in your pond. At all times. This means you need a reliable test kit or a meter. These are widely available and will generally report levels in either % or parts per thousand. Any test kit that reports concentrations in “color zones” or wide ranges is not worth the money you paid for it. For reference purposes: 1 ppt = 0.1%


Rule 4: Change salt concentrations SLOWLY. This means both directions. Slow up, slow down. Bring your salt levels up gradually over a period of days to your target. Bring them down over a period of weeks with water changes.

Rule 5: Don’t leave salt in when you don’t need it. ‘Nuff said.

Rule 6: Know how much salt to add before you add it. Hence the formulas.

Rule 7: Use the right salt. 99.9% pure or “Solar Salt” or “Blue Bag” salt. NOT pelletized or water-softener or road/sidewalk salt. Pickling salt is okay but way expensive and is for pickles, not fish. Pond salt or “aquarium salt” from the pet store is a flat ripoff. Iodized salt is expensive, and the iodine will injure gill tissue, just like its near-relative, chlorine (Look two spaces down from Cl in your handy-dandy Pocket Periodic Table). What you need is available from your local Home Despot equivalent for about 4 bucks per 50 lb. bag. It is evaporated sea water and contains other minerals (magnesium, calcium and others) which will act as buffers to stabilize your pond’s pH and will also supply trace minerals essential for koi health.

The “Not Rocket Science” Formulae:

Lb salt to add = (total gallonage of your system/120) multiplied by (desired salt conc. in ppt – current salt concentration in ppt)

For example:

Pond system volume: 4400 gal
Desired salt concentration: 1.5 lbs/100 gal = 1.88 ppt
Current salt concentration = 0.6 ppt

Lbs salt needed = (4400/120) x (1.88 – 0.6)

= 36.666 x 1.28 = 46.99 lbs salt

What is ultra-cool about this formula is that you can mess with it and get a formula to estimate the gallonage of your system. This is where an accurate test kit is critical.

Total gallonage of your system = 120 x Lb salt added / the difference between the salt concentration (in ppt) before and after you added the salt

To use the formula, you need to measure the salt concentration before and after you add a known amount of salt. Remember to give the salt enough time to thoroughly disperse throughout your pond. One day is just dandy. The amount of salt you choose to add will depend on the size of your pond and the accuracy of your test kit.

For example: A new pond. Medium to kinda big size. Good salinity meter from Aquatic Eco-Systems.

Starting salt concentration: 0.2 ppt

You add: 40 lb salt

Wait one day.

Final salt concentration: 1.0 ppt


1.0 – 0.2 = 0.8 ppt

Total gallonage = 120 x 40 / 0.8 = 6000 gallons


“Not Rocket Science”: Defined as the amount of math I can do without having to take off my shoes and socks.



So, here’s my recommendations:

Use salt sparingly, just like you would any other pond additive.


Monitor levels carefully. Don’t dose too high or change too fast.


Leave it in long enough to achieve your goal, then get rid of it with water changes.


© 2013 Robert D. Passovoy, MD