I've had two sea apples. They are always interesting and dangerous. I don't remember what happened or what I did with one but the last one closed up for weeks and then it sh!t an emerald crab, closed up again and since I like it so much, I moved it to my new tank and it died. They will loose all color and stayed closed, not like yours. When mine died it killed all my fish in one day or two. So, be careful, their beauty and novelty come with a price.