SALT, The Koi Wonder Drug?

by Norm Meck
reprinted from koiusa

Common Salt, Sodium Chloride, NaCI, has been termed "The Koi Wonder Drug". A misnomer perhaps, but salt is a proven staple in the health care and maintenance of Koi worldwide. Koi maintain an internal concentration of salt in their body fluids higher than that of their liquid environment. Osmosis causes water to transfer from the lower salinity of the pond water into the tissues of the fish. This additional water build up must be eliminated by the kidneys. Although salt in higher concentrations may slow some disease causing bacterial growth in the pond, the predominantly accepted theories ascribe the primary benefits of salt to lowering the osmotic pressure. This reduces the effort the fish must expend in eliminating the excess water. The saved energy is then available for use by the fish's own immune system to take care of other potential problems. The presence of salt also helps counteract any nitrite toxicity. In some cold climate areas, it is added in the winter to lower the freezing point of the water.

Salt can cause pond plant damage as the concentration increases. Floating plants, (water hyacinth, water lettuce, etc.) are affected at lower concentrations than most bog plants. Related, salt may provide some partial control of algae in the higher concentrations.

The amount of salt dissolved in water is measured either as a per cent, in parts-per-thousand (ppt), or in parts-per-million (ppm) (where 10 ppt = 1% = 10000 ppm). The more common parts-per-thousand measurement is the weight of the salt in pounds per thousand pounds of water (about 125 gallons). Pond-keepers often talk about the pounds of salt per hundred gallons of water. Since 100 gallons of pure water weighs about 800 pounds, one pound of salt per hundred gallons equates to a salinity of 1.25 ppt (0.125% or 1250 ppm). (1 ppt = 0.8 pounds per hundred gallons)

[Note: Koi internal fluid salinity is on the order of 15 ppt (about the same as ours) Sea water is around 35 ppt to 70 ppt depending upon geographical location. The Great Salt Lake has a nominal concentration of about 250 ppt.

There is some disagreement about salt in Koi ponds. Our San Diego tap water often has a salinity of up to 0.5 ppt. This amount cannot be tasted but we drink it and we put it into our ponds. If our Koi were put into an absolutely pure (distilled) water environment, the osmotic pressure would be so high that some would be unable to eliminate the excess water and would die almost as if by drowning. On the other hand, if the salinity approaches that of the internal tissues of the fish, the osmosis process will decrease or even reverse. This can cause the fish to die, essentially of dehydration. Any discussions should therefore center not on should salt be in the pond but how much.

The addition of one to two pounds of salt per hundred gallons of water (1.25-2.5 ppt) is recommended for most ponds, especially in the spring and fall. This is a fairly conservative dosage but without having a reasonable quantitative measurement method, higher concentrations should be avoided. If nitrites are present, using three to four pounds per hundred gallons (3.75 to 5 ppt)is appropriate to reduce the nitrite toxicity. After the initial application, the dosage applies ONLY to the amount of water being taken out and replaced, NOT to the amount of water in the entire pond. and NOT to water being added to replace that lost by evaporation. Except the very short-term medicinal baths at concentrations often around 25 ppt (1 pound per 5 gallons), and administered under tightly controlled conditions, it is not recommended that Koi be subjected to a salinity exceeding 5 ppt (4 pounds per hundred gallons), especially for extended periods.

The salinity is normally maintained by the addition of salt to increase it and by water change outs to decrease it. Introduce the salt. if possible, at the discharge side of the bio-filter (not at the bio-filter inlet nor directly into the pond). If the addition must be made directly into the pond, dissolve the salt in a bucket of pond water and distribute it evenly around the edges of the pond. Inquisitive Koi will check if any new addition to the pond might be something to eat. Although they will probably not swallow the pieces of salt, direct contact of crystalline salt with the fish for more than a few seconds can cause injuries similar to burns. When making the initial or any large application, it is probably better to divide it into two to four daily panial additions rather than putting it in all at once.

(Note: Inexpensive and pure solar dried or kiln-dried salt used in home water softeners is available at most supermarkets. Do not use pelletized water softener salt that has binding agents or any type of iodized salt.

I obviously am one of those who believe in adding salt to my Koi ponds. I am also one of those who do not like adding anything to the water unless I know what is already there. A pond-keeper can keep records of salt added, water removed, and water added. But, after a few water change outs, rain storms, and other water additions, the resulting salinity is somewhere between questionable and unknown. For some time, I have been trying to find a way to measure the amount of salt in my ponds. A chemical laboratory can supply a quantitative analysis, but this is both expensive and not very timely. Other than very expensive reflectometers, the commercial salinity test kits and other devices, available seem to measure in only two ranges. The first is around 0-50 ppt, used for salt water systems and the second is around 0-100 ppm used for fresh water applications. Neither of these will provide the accuracy needed over the range of interest. I would like to maintain a concentration in the range from 2.0 to 4.0 ppt (I actually use a target of three ppt or 2.4 pounds of salt per hundred gallons).

In cooperation with the LaMotte Co., a leader in aquaculture testing products.., a modified procedure was developed for use with one of their salinity test kits to provide a fast, inexpensive, and highly accurate measurement over the desired range. The "off-the-shelf' kit was designed to measure 0-20 ppt in 0.4 ppt increments. Substituting the modified test procedure provided below for the standard procedure, the range is changed to 0-5 ppt in 0.1 ppt increments. The titrator supplied with the kit reads 0-20 and the result is divided by four. An optional titrator, calibrated 0-50, can be purchased and the result divided by ten, which is a little easier. It probably makes little difference to the fish, but I feel better that I can now make an accurate salinity reading.

As an example of the accuracy of this test and as a secondary use of the test kit, a pond was found to have a 0.5 ppt salinity measurement. It was desired to bring the level to 2.5 ppt, an increase of 2 ppt. As the owner thought the pond contained about 3100 gallons, 50 pounds of salt was added (3100 divided by 125 times 2). The next day, the salinity actually measured 3.1 ppt, or an increase of 2.6 ppt. Working backwards, this showed that the pond actually contained only 2400 gallons (50 times 125 divided by 2.6). A later unfortunate incident required the pond to be drained. When it was refilled through a water meter, it was determined that the pond actually held just under 2500 gallons. The pond owner had been excessively medicating and chemically treating the pond by almost 25%! It has been found that the salinity test kit can be used to determine the amount of water in a pond with an accuracy of about 5%.

If you purchase the test kit for use in the 0-5 ppt range. use the following test procedure, (see insert) not the one included in the kit.

The salinity test kit (Part No. 7459: about $35 for 50 tests), the refill kit (Part No. R7459; about $15 for 50 tests), and the optional 0-50 direct reading titrator(Part No. 0380; about $5), are available directly from LaMotte or, at an equal or slightly lower cost, from one of their distributors listed below (or others). Prices do not include shipping, and are, of course, subject to change. All will accept major credit cards.

Modified Test Procedure for LaMotte Salinity Test Kit Model 7459

1. Rinse and fill the titration tube to the 10 ml line with deminenalized water from the demineralizer bottle.

2. Rinse and fill the 1.0 ml Direct Reading Titrator to the zero mark with the water to be tested. Wipe any excess water off the Titrator.

3. Dispense the entire 1.0 ml of sample water into the titration tube. 4. Repeat steps 2 and 3 to add a second 1.0 ml of sample water into the titration tube.

5. Add 3 drops of Salinity indicator Reagent A to the titration tube. Cap and gently swirl to mix. A light yellow color will develop.

6. Fill the 0-20 (or optional 0-50) Direct Reading Titrator to the zero mark with Salinity Titration Reagent B. Insert Titrator in the hole of the cap of the titration tube.

7. While gently swirling the tube, slowly depress the plunger until the yellow color changes to pink-brown. 8. Read the test result where the plunger tip meets the scale on the calibrated titrator.

9.If using the 0-20 titrator supplied with the kit, divide the reading by four (i.e. if the titrator reading was 9.2, the result is 2.3 ppt). If using the optional 0-50 titrator, divide the reading by ten (i.e. if the titrator reading was 23, the result is 2.3 ppt).

(Note: The demineralizer bottle can be refilled with tap water or even pond water but the deionizing resin bed will last longer if distilled water is used.

Note from Chuck: I have this kit but I have also seen a nice test kit at Pet supermarket  by Pond care: