Ich (Ichthyophthirius multifiliis) Treatment Guide

Ich is caused by the ciliated protozoan Ichthyophthirius multifiliis; without treatment mortality can approach 100%. Only the free-swimming theront stage is treatable.

Overview

Ich, also called White Spot Disease, is caused by the obligate ciliated protozoan parasite Ichthyophthirius multifiliis (phylum Ciliophora). The parasite has a three-stage life cycle: the trophont feeds inside the host's skin and gill epithelium, the tomont detaches and forms a cyst on substrate, and the theront is the free-swimming infective stage that re-infects fish. Only the theront stage is vulnerable to treatment. In untreated infections mortality can approach 100%.

Symptoms

White salt-grain spots on body and fins
Flashing (scratching against decor and substrate)
Clamped fins
Rapid gill movement and laboured breathing
Lethargy and balance disturbances
Loss of appetite

Causes

Outbreaks are triggered when the parasite enters a tank on newly added fish, plants, or water that has not been quarantined. Stress factors such as temperature swings, poor water quality, transport, and aggression suppress fish immunity and allow theronts to establish. The parasite affects most freshwater species with low host specificity.

Diagnosis

Ich is diagnosed visually by characteristic salt-grain white dots roughly 0.5-1 mm in diameter on body and fins, combined with flashing behaviour. Differentiate from Epistylis (stalked protozoan, cottony tufts) and Saprolegnia (cotton-wool fungus, secondary to injury) — both look fluffier and grow on damaged tissue rather than as discrete points.

Treatment

Step 1: Quarantine

Move affected fish to a bare-bottom quarantine tank if possible. If the entire display is infected, treat the whole system after removing invertebrates, sensitive scaleless species and live plants where applicable. Remove activated carbon, which absorbs medications.

Step 2: Medication

Heat-and-salt protocol: raise temperature gradually to 30 C (86 F) and add aquarium salt (sodium chloride) at 1 tablespoon per 4 L for 10-14 days, continuing 3 days past the last visible spot.
Formalin + malachite green combination per package directions every 24 h with 25% water change between doses for 10-14 days. Malachite green is banned in food fish in some jurisdictions.
Copper sulfate per package directions in fish-only systems; not safe for invertebrates or live plants.
Strong aeration during all chemical treatments — medications and elevated temperature both reduce dissolved oxygen.

Step 3: Recovery

Continue treatment for at least 3 days after the last visible spot — encysted trophonts under the skin are protected and only newly released theronts can be killed. Restore activated carbon, perform a 30-50% water change, and lower temperature gradually over 2-3 days. Boost fish immunity with high-quality varied food.

Prevention

Quarantine new fish and plants for 4 weeks
Avoid temperature shock during water changes
Maintain stable water parameters
Disinfect wild-collected plants before introducing them
Feed a varied high-quality diet to support immunity