I have always read/heard that 'ich' is a freshwater ectoparasite.
http://en.wikipedia.org/wiki/Ichthyophthirius_multifiliis">http://en.wikipedia.org/wiki/Ichthyophthirius_multifiliis</a>
Amyloodinium, or just oodinium, is sometimes called 'saltwater ich' or referred to as 'velvet' as well, due to it's small size.
[IMG]http://reefkeeping.com/issues/2004-07/sp/feature/index.php">http://reefkeeping.com/issues/2004-07/sp/feature/index.php</a>
Cryptocaryon, also called 'white spot' is a larger external parasite.
[IMG]http://en.wikipedia.org/wiki/Cryptocaryon">http://en.wikipedia.org/wiki/Cryptocaryon</a>
Brooklynella, is yet another external parasite of the ciliated prozoan variety. Formalin is said to be effective.
I have had great success using quinine compunds in the past (quinacrine hydrochloride, quinine sulfate). The OTC/retail source went out of business years ago.
I found these folks below, and they develop and market aquatic pharmaceuticals for a living. They are a resource for most aquariums and universities in the country.
They sell quinine sulfate, and claim it to be the best/most reliable treatment they have. It will treat ALL OF THE ABOVE (I will be ordering)-
[IMG]http://www.nationalfishpharm.com/articles/brooklynella.html">http://www.nationalfishpharm.com/articles/brooklynella.html</a>
It is also well tolerated by the fish.
FWIW- quinine derivatives are used to treat malaria as well.