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Translated in Dutch by Joost Abrahams

10.2. Skin Protozoans

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Author : David Bogert

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1 minute
Difficulty : Level 6

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What are the tiny white spots on my fish?

Skin protozoans, namely ich, are without a question the most common disease in fish. Treating ich and most skin protozoan diseases is actually very easy.

Public Aquariums use formalin/malachite green (Ich-X, Rid-Ich Plus, Blue Planet White Spot Remedy and Mardel QuickCure) to treat ich in freshwater fish, as do University Research Centers, Cory of Aquarium Co-op and Joey.


  1. Formalin/malachite green is poisonous if one overdoses
  2. One should never raise the temperature with formalin/malachite green.
  3. Never turn off the filter, change the filter media or clean the filter media with ich
  4. Do not move the fish to a hospital/quarantine tank
  5. Cory and others have treated thousands of “scaleless” fish with full strength formalin medication with absolutely no problem.

The seminal study on ich treatments (Tieman and Goodwin, 2001) found salt and heat to have no effect on ich.

Most of the external protozoans of fish are delved into in some depth in the following chapters:

10.2.1. All Skin Protozoans

10.2.2. Ich

10.2.3. Velvet

10.2.4. Epistylis

10.2.5. Chilodonella and Costia

10.2.6. Tetrahymena

10.2.7. Cryptobia