Freshwater Tropical · Goldfish

Freshwater Ich (White Spot Disease)

The most common freshwater fish disease. Tiny white spots resembling grains of salt cover the body and fins.

Severity: Moderate

*Ichthyophthirius multifiliis* is the most familiar freshwater parasite. The trophont stage embedded under the skin appears as white salt-grain spots; once it drops off and divides as a tomont, the released theronts re-infect the host. Only the free-swimming stage is vulnerable to treatment — which is why temperature-driven life-cycle acceleration matters.

Causes

Almost always introduced via new fish. Stress and low temperature reactivate latent infections. Common in pet-store stock that has been bagged repeatedly.

Treatment

Raise temperature gradually to 28–30 °C (82–86 °F) to speed up the life cycle. Treat with **Forma-Green** or malachite-green + formalin for 10–14 days. Continue 5 days after the last visible spot disappears — invisible tomonts are still cycling.

Recommended medications

Prevention

Quarantine new fish for 2–3 weeks. Maintain temperature stability. Avoid chilling stress during water changes.

Frequently asked questions

Why did the spots come back after treatment?

You stopped treating too early. The visible spots are only one life stage. Treat for at least 5 days past the last visible spot to break the cycle completely.