The anemone is fine without the clown, and the clown without the anemone. The random outbreak is why ich is such a problem. It was always in your tank, (when you added one of your fish) The second you introduce a fish into your system you run a 50% chance of having a parasite, add more than one and obviously your chances are greater if not certain. The parasite can easily be in your tank for months before you see anything. They are more likely to attach to the gills than anywhere else. There are theroies that suggest the reason you are finally seeing them is because the gills are completely overrun. Which could stand to reason. After the QT of the clown and tang ALWAYS Qt everything that goes into the tank. Inverts, rock, sand, of course other fish for atleast a month. You don't have to treat the inverts or inanimate but you should treat all fish for good measure. Have you considered the treatment you will be using? I would suggest reading the top threads, the ones that are stickied