Salt as a Treatment for Fish

Salt is a common and relatively inexpensive treatment for fish. The use of non-iodized table salt or rock salt (suitable for consumption by humans or livestock) is acceptable for treatment. For ease of application, many pond owners use 50 lb salt brine blocks. "Brine" blocks are salt blocks. Granular salt can also be purchased in bags or bulk.

Seawater contains 3% (30,000 ppm) salt concentration. Two hundred ppm (200 ppm) to 500 ppm can be used as an indefinite treatment in ponds to relieve stress. Ten thousand ppm (10,000 ppm) to 30,000 ppm can be used as a prolonged treatment in tanks for 30 minutes or until fish show signs of stress. Thirty thousand ppm (30,000 ppm) can also be used as a quick dip (60 seconds) in treatment tanks. To achieve 30,000 ppm in a tank, you add 2 1/2 lbs of salt for every 10 gallons of water. For ponds, 1 ppm is equal to 2.7 lbs/acre-ft of water. You need to know how many acre-feet of water you have in your pond (surface acres x average depth) to determine the treatment rate.

How Much Should I Treat?

How much should I treat with? That is often the first question one asks when a treatment is necessary. Fish diseases require different treatments at different rates. Identifying the fish disease is the first step. There are several North Carolina Department of Agriculture Animal Disease Diagnostic Laboratories across the state to help in identifying the disease problem.

Once the disease is identified, a treatment can be recommended. Applying the correct treatment at the required rate is necessary to remedy the fish disease. But the question still remains...how much should I treat with? This is because most pond owners do not know the size or the average depth of their pond.

Do you know the size of your pond? What is the average depth? There are methods to help to determine the surface acreage of your pond and the average depth.

Rectangular or square ponds can be measured by pacing or a tape measure. The length and width of the pond needs to be measured.

Surface area = length (feet) x width (feet) = area ft²
Area = ft²/43,560 ft² = surface acres

If the pond is circular, the circumference needs to be measured. The circumference is the distance around the shoreline.

Surface area = circumference (feet) x circumference (feet) = area ft²
Area ft²/547,390 = surface acres

Many ponds are irregularly-shaped. Approximate the pond shape as either square, rectangle, or circle by measuring the boundary lines that most nearly represent the actual shoreline. This pond shape can be approximated as a rectangle.



Surface area = length (feet) x width (feet) = area ft²
Area ft²/43,560 ft² = surface acres

If the pond is triangular, the base and the height should be measured. Multiply those two numbers, take half of the resulting amount, and divide by 43,560.

Surface area = width (feet) x height (feet)/2 = area ft²
Area ft²/43,560 ft² = surface acres

Average Depth Calculation

Average depth can be determined by taking uniformly-spaced soundings over the entire pond surface. This can be done from a boat. The measurements can be taken with a long pole, chain, or weighted rope marked off in feet. At least 15 measurements should be taken. Add the measurements and divide the number of measurements taken.

Frequency of Measurements

Pond measurements should be re-taken whenever there is an appreciable change in either surface area or average depth. Significant changes in surface area occur when existing ponds are enlarged. However, average depth changes very gradually over a period of years as a result of natural processes. Sediment inflow and the accumulation of decomposing vegetation will cause a pond to gradually become shallower. A pond that may have been 15 feet deep when it was constructed may only be 10 feet deep after several years. Average depth should be re-calculated every five years to account for gradual filling in of the pond. Soil disturbances in the watershed or excessive accumulation of decomposing vegetation in the pond will require more frequent measurement of the water depth.

Let's Make Some Pond Measurements

I would like to offer my assistance in making your pond measurements. We can have on record how big your pond is. When making treatments, you can start with a better estimate of how much to treat. All you need is a boat or canoe to take us over the pond surface. Please contact me to schedule an appointment.