Koi Flashing and Ulcer: Parasite Treatment Protocol

Symptoms

12×20×3 ft pond, 17 fish. Flashing (scratching). Treated with "Terminate" (likely formalin/malachite green) – killed algae and biofilter. Now flashing again, large koi has lifted scale and ulcer.

Immediate Actions

1. Stop feeding until biofilter recovers (ammonia/nitrite = 0).
2. Add bottled nitrifying bacteria (FritzZyme, Seachem Stability) daily.
3. Test ammonia/nitrite 2× daily.
4. Do 10% daily water changes with dechlorinated, temp-matched water.

Parasite Treatment

• Ich (white spots): Formalin/malachite green (e.g., Jungle Ich Guard) – safe for biofilter if used correctly.
• Flukes (no visible spots): Praziquantel (PraziPro, Aqua Prazi) – safe, effective.
• Costia/Trichodina: Potassium permanganate (PP) – oxidizes parasites, but kills biofilter. Use only in quarantine.

Ulcer Care

Topical iodine/povidone on ulcer. Injectable antibiotics (vet) if deep. Salt bath (0.3%) helps osmoregulation.

Diagnosis

Microscope scrape essential. Guessing wastes time and money.