The disease is caused by a protozoan parasite, Ichthyophthirius multifiliis, and is very contagious.
The parasites spend a portion of their life cycle embedded beneath the skin of the fish, where they feed from
the body tissue. The white cyst in which they are enclosed gives the characteristic white spots. Adults emerge
from these cysts and fall to the floor of the aquarium, where they multiply inside a protective capsule. Some time
later, the capsule bursts, releasing hundreds of free-swimming infectious parasites which attach themselves to
new hosts. Whitespot is often introduced with new fish which have not been quarantined. Outbreaks of whitespot
often occur after fish have been exposed to cooler than normal temperatures. Clown loaches are particularly prone
There are two main approaches to curing whitespot, and opinions vary on which is the more effective.
There are several effective commercially available remedies, normally based on malachite green and formalin. Note that
malachite green is hard on scaleless fish like catfish and loaches, and also other fish such as tetras. Some alternative
medications are based on copper and formalin.
The other method employed is to add salt to the tank (gradually), up to a level of 6-8 tsp per gallon. Note that fish
vary in their tolerance of salt, and for more sensitive soft-water species, it may be better to use 3-4 tsp per gallon
maximum. Higher salt levels may also affect plant growth.
In either case, increasing the temperature should kill the parasite off more quickly, because it will
speed up the life cycle of the parasite, so that the free-swimming stage is reached as quickly as
possible - this is the only stage affected by medications. However, increasing the temperature means there will
be less oxygen dissolved in the water (some medications can lower it too), so ensure the tank is well aerated,
and do not raise the temperature beyond around 28oC (82oF).
Due to the life cycle of the parasite, the whole tank must be treated, in order to kill the parasites which are
not attached to fish. Therefore it is not appropriate to treat only the affected fish in a separate isolation tank.
Effective commercial remedies include Protozin by Waterlife and Maracide by Mardel Labs. In more recent times, resistant
strains of the whitespot parasite seemed to have emerged, some of which are difficult to treat - it may be necessary to try
a different treatment if the medication is not effective within 6-7 days.