If your water quality is less than great a feather duster will lose its crown. I is a weird process. the tips will curl and then the crown will drop off like someone came along with a pair of scissors. remove the dead crown or let some hermits snack on it. you wont see any activity from the feather duster until water quality goes up (do several waterchanges this month, one a week would be great.) after about two to three weeks you will see a light off white crown that is about half the original size. wait another week or two and the color will start to return. it wont have the original color. my feather duster used to have alternating purple and cream bnds, now its half brown and white. white center with brown tips. so dont worry, its not dead. if nothing happens within a month, i would assume that it died. they are really sensitive to water conditions.