Our next parasite under discussion is leeches.
They can often be found in ponds where there are a lot of plants and are normally introduced to the pond via plants. Therefore it is very important to dip any new plants with Trichlorfon (Dipterex or Masoten) or Dimilin. Potassium is not very effective in killing them.
They are also often introduced by birdlife.
They are not a very serious threat but should be removed as it can cause problems in the long run.
Sludge in a pond is an ideal breeding ground for them, so sludge should always be prevented.
They can grow as big as 8 cm in length and often attach themselves to the bottom of the koi where there are no scales and therefore they are often difficult to spot.
It is quite difficult to get rid of them once your pond is infected. Numerous treatments with Dimilin or Trichlorfon are required because the treatment will not kill the eggs. You will have to wait until they hatch.
You also need to physically remove them from the koi and treat the area where it attached itself with Malachite green or Methylene blue and Friars balsam to prevent infection.
As an alternative, you can set traps for them.
1.) Take a bucket with a lid.
2.) Poke holes in the sides of the bucket. Holes should be 1 cm in size.
3.) Put some raw meat in the bucket.
4.) Put the lid on and submerge it completely in your pond.
5.) Remove the trapped leeches from the bucket.