Ya, one day they just started to close up with a few just half open. They did not outright die. Fortunately, after moving them around, water changes etc. I met a private owner of a saltwater businesses and he said perhaps your iodide trace is to low. Zoas need a little iodine as this acts like a growth hormone.... But if I would of not figured this out surely they would of died.Mine too. But I was not seeing rapid melting, just a noticeable reduction in the hours the polyps would stay open.