Salt to Kill Giardia in Koi Ponds

Koi ponds are beautiful, but can harbor dangerous parasites.

Giardiasis (pronounced gee-are-DI-uh-sis) is a parasitic infection of the small intestine that causes diarrhea in humans and animals. It thrives in standing or slow-moving water such as in fish ponds and is a common cause of waterborne disease in humans. Among the many ways that koi pond owners have tried to kill the Giardia lamblia parasite is the use of salt. The EPA lists possible disinfectants in order of tested effectiveness: ozone, mixed oxidants, chlorine dioxide, iodine, free chlorine and chloramines.

Effectiveness of Salt on Giardia

Giardia lamblia is a tenacious parasite to eradicate. Because of its ability to encase itself in a hard shell called a cyst, it is impervious to most disinfectants including salt. In fact, researchers often use a heavy solution of salt and water called Hank’s Balanced (or Buffered) Salt Solution to rinse giardia cysts in preparation for study in the lab. The use of salt in a koi pond will not eradicate giardia.

Salt and Koi

Koi need salt to maintain their electrolyte balance and to build a slime coating on their skin that resists parasites. Koi enthusiasts typically keep their ponds’ salinity at a concentration of 0.18 percent (1.8 parts per thousand) or 1 pound of salt per 100 gallons of pond water under normal conditions. When treating sick fish, though, veterinarians advise removing those fish to an isolation tank and increasing salinity to 3 lbs. per 100 gallons. This concentration will kill fish parasites, but will have no effect on giardia.

Ozone or Mixed Oxidants

Electrolysis, or passing an electrical current through plain water, generates ozone. Passing current through salt brine (water with a small amount of dissolved salt) generates mixed oxidants (brand name MIOX; EPA abbreviation MOGOD.) Both ozone and mixed oxidants have been shown to be effective against giardia, but require equipment that may be too expensive and complicated for fish pond owners. Remove all fish and plants from the tank before treatment, and filter out deposits before returning fish and plants to the tank.

Chlorine

Researchers at the University of Oregon studied the viability of giardia cysts in chlorine and water testing variations in temperature, acidity (pH) and time spent in the solution. The study showed that chlorine in a concentration of 1.5 milligrams chlorine per liter of water can kill giardia in 10 minutes if the water is at least 77 degrees Fahrenheit. Lower temperatures or lower concentrations of chlorine require longer times, for example up to 60 minutes for 52 degree water. All fish and plants should be removed before treatment with chlorine.

References

• EPA: Giardia, Drinking Water Health Advisory
• U.S. Department of the Interior, Bureau of Reclamation: Water Treatment Primer
• Centers for Disease Control: Giardia
• "Applied and Environmental Microbiology"; Effect of Chlorine on Giardia Lamblia Cyst Viability; E.L. Jarroll, et al.; March 1981
• Waterborne Pathogens; Giardia; Lucy Robertson, et al.; February 2010
• B.F. Environmental Consultants Water Research Center; Ozone in Water Treatment; Brian Oram

Resources

• National Fish Pharmaceuticals: Koi Pond General Information
• Simi Koi: Salt in Koi Ponds
• Diet.com: Giardiasis