Diagnosing a Single White Bump on a Koi in a Large Pond

Single Spot ≠ Ich

Ich = hundreds of tiny white dots. One bump is different.

Injury + Infection: Scrape from spawning, rock, net. Bacterial/fungal secondary.
Anchor Worm / Fish Lice: Parasite attached or recently detached leaving a wound.
Color Change: Koi patterns shift; a white patch may be new pigment.
Fish TB (Mycobacterium): Boil-like lumps, chronic wasting.
Viral (Lymphocystis, Carp Pox): Wart-like growths; usually benign.

Net only if fish shows distress. Observe. If bump grows, ulcerates, or multiplies, quarantine and treat with salt + antibiotic. See health guide.

Pond and Water Gardening: Winterizing a Koi Pond in North Carolina; Koi Behavior in Cold Water: Surface Hovering; Clearing Green Water in a Koi Pond: Nutrient Control Is Key; Black Water in a Koi Pond: Test pH and Nitrite First; Foam Around Pond Edges After Algaecide: Overdose or Surfactant?; Koi Floating on Side: Swim Bladder or Something Worse?; New Pond Owner Loses Koi: Common Mistakes and How to Avoid Them; Koi with Large Body Holes: Disease, Toxins, or Cement Pond Issues?; Koi Swimming Sideways: Swim Bladder Disorder and Quarantine Treatment; High Altitude Koi Pond: pH Obsession vs. Nutrient Control

Garden Articles

Plants