You may not need to take your tank down Paul, if you keep searching there are ways people have gotten rid of them. I've had success using Aptasia X using a syringe, others have used kalk paste (same as Aptasia X), or peppermint shrimp, or copper band butterflies, there are other ways too.
There was a poll recently on what methods people have used and whether they had success or not. They're unsightly, spread rapidly, and can sting corals so they're not an ideal pest to have, but don't be discouraged. They can be beat
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