Marine / Saltwater
Marine Ich (Cryptocaryon irritans)
Saltwater white-spot disease. A 2006 resistant strain renders traditional copper and formalin treatments ineffective — quinine sulfate is the only reliable cure.
Severity: Severe
*Cryptocaryon irritans* is the saltwater analogue of freshwater ich. White cysts appear on the skin and gills; the protomont stage drops off to encyst on substrate, then releases dozens of free-swimming theronts that re-infect the host.
A **resistant strain** appeared in 2006 that is impervious to formaldehyde, malachite green, copper, and the common organic dyes. For this strain, **quinine sulfate is the only reliable treatment**.
Causes
Introduction of unquarantined fish. Suppressed immunity from elevated nitrates or rapid salinity/temperature changes. Once present, the parasite cycles through the tank for weeks if untreated.
Treatment
Quinine sulfate at 16.5 mg/L (62.5 mg/gallon) for 14 days in a quarantine tank. **Never** treat the display tank — quinine kills invertebrates. Maintain copper at 0.15–0.20 ppm for 14 days as an alternative for non-resistant strains, but verify with a hobby copper test daily.
Recommended medications
Marine Ich (Cryptocaryon irritans)
Saltwater white-spot disease. A 2006 resistant strain renders traditional copper and formalin treatments ineffective — quinine sulfate is…
Prevention
Mandatory 4-week quarantine for every saltwater addition, including corals (rinsed and dipped). Hyposalinity (1.009 SG) for 6 weeks pre-introduction is also effective.
Frequently asked questions
Why didn't copper work on my fish?
A copper-resistant strain of Cryptocaryon emerged around 2006 and has since spread widely. Quinine sulfate is the only reliable treatment for it.
Can I treat marine ich in my reef tank?
No. Every effective treatment will kill your invertebrates. Move fish to a bare-bottom QT and let the display run fallow for 76 days.
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Marine / Saltwater
Marine Ich (Cryptocaryon irritans)
Saltwater white-spot disease. A 2006 resistant strain renders traditional copper and formalin treatments ineffective — quinine sulfate is…
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Marine / Saltwater
Marine Ich (Cryptocaryon irritans)
Saltwater white-spot disease. A 2006 resistant strain renders traditional copper and formalin treatments ineffective — quinine sulfate is…
Severe
Marine / Saltwater
Marine Ich (Cryptocaryon irritans)
Saltwater white-spot disease. A 2006 resistant strain renders traditional copper and formalin treatments ineffective — quinine sulfate is…
Severe