Originally Posted by crister13
Ick has to be introduced into the system. Also, a cleaner shrimp won't cure it or eating at all because ick is under the skin, and cleaner shrimp only eat things on the skin. The spots are a reaction to it.
With all due respect, I'm not sure where you are getting your information.
Oodinium and cryptocaryon (a.k
.a. Saltwater Ich) are external parasites and are known to be carried by both fish and some inverts such as corals and anemones. (Yet another reason to quarentine new arrivals.) Older research found that the parasite Oodinium once introduced in a tank, can last over 4 weeks without a host fish. Fish left unmedicated in an oodinium exposed tank are extremely susceptible to infestation.
Cryptocaryon does have a more advanced stage when the parasite burrows into the flesh of the fish thereby making medicating a harder task. Early detection and treatment are extremely important when dealing with this organism. In certain fish, Tangs being one of them, the secreting of excessive mucus to protect the skin actually makes medications ineffective against the parasite whereby a cleaning shrimp would be a benefit to help expose the parasite and remove it from the skin. At this point, secondary infection (bacterial or fungal) will be the next threat.
This is, once again, why it is so important to quarantine new arrivals for a minimum of 3 to 4 weeks if medicated and 8 weeks or longer if not being medicated.
I suggest you do some more research on parasitic organisms so you can better prepare yourself and can help others.