What is the cause for a goldfish to have Ick disease one week and the next to have the torn fin?

Sorry for my late replyThere are one rule that you should keep in mind:Never populate tropical fish along with gold fish, They are extremely sensitive to each other diseases, and the most important thing is that they both need different water conditions.

I am not sure about the tornfin disease but I know of two ways your fish could have gotten Ick. First, and most likely, is that the new fish you introduced to the tank exposed the other fish. I have found over the last two decades of keeping fish that a new fish can wipe out an entire tank.As a result of said knowledge, I would sugest setting up a small isolation tank for new fish to dwell in for at least a week upon purchasing them.

Secondly, temp. Changes in the tank can cause Ick esp. If it drops too much or too fast.

I hope this helps some.

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