How much flow do you have going through the tank? What are you parameters? Salinity/ph/nitrate/phosphate?
They will often wander around till they find a spot with the right amount of light and flow to their liking. If it isn't finding a spot you could have too much flow, too much or not enough light. Can be a number of things. They are sensitive.
Welcome to the world of nems. First off yours looks bleached. Secondly nems are going to go where they are happy. They like lots of light and a fair amount of flow. If you could please post your parameters - SG, alk, cal , temp, nitates, etc...