Copper Treatment for Marine Ich and Velvet: Dosing, Testing and Dangers

Copper is the standard treatment for marine ich (Cryptocaryon) and marine velvet (Amyloodinium), but it has a narrow safe window and is lethal to invertebrates and corals. Learn the therapeutic range, why you must test copper constantly, and why it belongs only in a bare quarantine tank.

Copper is the standard for marine parasites

Copper is the mainstay treatment for the two most dangerous marine external parasites: Cryptocaryon irritans (marine ich or white spot) and Amyloodinium (marine velvet). It kills the free-swimming stages of these parasites, but only within a narrow concentration band, and it must be used carefully to be both effective and safe.

Therapeutic range and testing

• University sources give a therapeutic level of about 0.15-0.20 mg/L free copper (Cu2+) for marine parasites, brought up gradually over two to three days.
• The window is narrow: around 0.3 mg/L, copper starts to inhibit the ammonia- and nitrite-oxidizing bacteria of the biofilter, so ammonia and nitrite must be watched.
• Copper must be measured with a test kit at least twice a day and re-dosed, because it is constantly bound out of solution.

Why it must be a bare quarantine tank

Carbonate materials - crushed coral, oyster shell, aragonite substrate and live rock - dissolve and bind copper, dropping it below the therapeutic level, and activated carbon removes it entirely. Copper is also highly toxic to invertebrates and corals, which will not survive treatment. For both reasons, copper is used only in a bare-bottomed quarantine or hospital tank, never in a display reef.

Duration must outlast the life cycle

Because only the free-swimming stage is vulnerable, treatment has to span the parasite's full life cycle: university guidance gives about three to six weeks for Cryptocaryon and roughly 10-14 days for Amyloodinium, with copper held continuously. Lowering salinity (hyposalinity, on the order of 15-18 g/L) is a commonly used adjunct. Ionic copper (copper sulfate) and chelated forms behave differently - follow your specific product's instructions and test kit.

Sources: UF/IFAS FA165, Use of Copper in Marine Aquaculture and Aquarium Systems (ask.ifas.ufl.edu); UF/IFAS FA164, Cryptocaryon irritans (ask.ifas.ufl.edu); Merck Veterinary Manual, Parasitic Diseases of Fish (www.merckvetmanual.com).