Ich

Freshwater Ich (Ichthyophthirius multifilis) is a ciliated protozoan that encysts under the epidermis of the fish; and, in its encysted condition, causes small white spots all over the fishes body and fins. In some cases, Ich spots may be present, but will not be visible.

Ich rapidly kills smaller tropicals and goldfish, while often sparing the larger varieties (fish such as Oscars and Koi). Damage to the gills is the primary way it kills, but damage to the skin with secondary bacterial infection may also figure prominently.

The parasite has a phase that encysts in the epidermis of the fish as previously stated (called a theront).

Salt is the treatment of choice for Ich. See salt article.
How long do I leave Salt in the water?
Fourteen to 21 days may be required to totally eradicate certain parasites at certain temperatures. Rest assured, it could stay in the water forever. But for Ich it could also be removed within seven days and recurrence of Ich would be unlikely if temperatures during treatment were around eighty degrees F. Ten to fourteen days is suggested 'for best results' with Ich.

To recap my points, here's the nuts and bolts of Salting Ich..

• 1. Remove valued live plants.
  
• 2. Raise temperature to 80 degrees, tops.
  
• 3. Increase aeration!
  
• 4. Add one teaspoon of salt per gallon.
  
• 5. Twelve hours later, add another one teaspoon of salt per gallon.
  
• 6. Twelve hours later, add another one teaspoon of salt per gallon.
  
• 7. Within 48-60 hours of the second salt dose at 80 degrees, the Ich will be gone.
  
• 8. Leave salt in the water for another 3-5 days unless you're worried about your live plants.
  
• 9. Remove salt via partial water changes. (30-40% at a time if desired).
  
  

The Ich organism under the scope.