Catching a tang...

[mandyplo]

Originally Posted by gregzz4

You meant to say it often goes unseen, right ?
ICH is either in a tank or not

I'm not a scientist (yet) but I think hes right when he said it lies dormant (in a way). Ich, from what I know about freshwater and assume is similar to saltwater, is that every fish either has been exposed to ich at one point in its life or has it, and most tanks always have the ich parasite present in their water. The only time the fish is actually affected by it is when their slime coat is reduced, caused by many things. Most commonly stress. When a fish is at its healthiest, the ich parasite cannot penetrate the fish's slime coat and affect the fish. But as soon as a fish is feeling down the ich is able to take advantage.

This is why the OP needs to get the other tang out of the tank, so the tang can be relieved of stress and fight off the infection on his own. Once he is healthy and back to normal, the ich will still always be in your water, but it won't affect your fish unless they become stressed/sick from another cause.