How to Treat Gill Maggots in Koi

Gill maggots are tiny gray-black and white parasites that are the mature female form of the crustacean Ergasilus. Their name comes from the maggot-like appearance of their egg sacs. Gill maggots are commonly found in outdoor pond koi during the summer months. Koi that have gill maggots will flash up out of the water and gasp for air at the surface. You can treat your koi effectively and eliminate gill maggots without resorting to hazardous insecticides.

Things You'll Need

  • Parazoryne concentrate
  • Thermometer
  • Pond water heater
  • Bucket, 2 gallons
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Instructions

    • 1

      Turn off any ozone generators, protein skimmers, algae magnets or UV sterilizers that you use to treat your pond water. Remove the carbon and zeolite from pump filters. Leave any biological filters in the pump and keep it running.

    • 2

      Measure the water temperature. The pond water needs to be at a minimum temperature of 71 degrees Fahrenheit. If it is not, use a water heater to bring the water to the proper temperature for the parazoryne to work.

    • 3

      Scoop up one gallon of the pond water with the bucket. Add one teaspoon of parazoryne per every 125 gallons of water in your pond to the pond water in the bucket and stir it thoroughly. Let it sit for 10 minutes to ensure that the concentrate disperses evenly.

    • 4

      Add the treated water to the pond water by distributing it around the pond as evenly as you can, pouring a thin stream of the solution as you walk the perimeter of the pond. Treat the pond water with parazoryne for the next 10 days. If you don't see an improvement, continue treatment for another week.