Marine Ich vs. Freshwater Ich: Key Differences

Despite sharing a common name and similar symptoms, marine ich and freshwater ich are caused by entirely different parasites and require different treatment approaches.

Freshwater Ich

Caused by Ichthyophthirius multifiliis, freshwater ich is generally treated with heat and medication as described in our freshwater ich treatment guide.

Marine Ich

Caused by Cryptocaryon irritans, a different organism entirely, marine ich is typically treated with copper-based medications, hyposalinity, or specialized reef-safe alternatives — but always in a separate quarantine tank given the toxicity of copper to invertebrates, as discussed in our copper medication guide.

Shared Prevention Principles

Both parasites are far easier to prevent than treat — proper quarantine (see why you need a quarantine tank) dramatically reduces the risk of either disease reaching your main display.

Why the Distinction Matters

Using a freshwater ich treatment on a marine tank (or vice versa) won’t be effective, so correctly identifying which type you’re dealing with is an essential first step.