check you water parameters and temps. They usually vacate tubes if the water is bad or they can't get food where they are at. I would isolate it from any hermit crabs or fish that might pick at it until it makes a new tube. You want the water flow to go through the back of the feathers that is the way it feeds. E.G. if you spot feed it, squirt the food behind the duster and let the flow carry the food into the feathers.