Hi
Do not force the Achilles to eat. It will do it when it so pleases. Feed it soft algae in small bits. Just give the algae and go on with your life and let it be swimming calmly and choose the bits when it so pleases, and do not stress as it will feel your stress and suffer from it so if you want to observe it eating or swimming, just do it from distance in a way that it does not feel it is being observed... I have quite some experience with more sensitive fish such as the Zanclus, and know about this ... this said I do not know your experience ... but you will be successful I believe. These are quite sensitive at first but when well aclimated, they are very resilent. By the look in the photo you have a very strong and healthy specimen. Well these are suggestions ... and fortune favours the bold ... good luck and all the best are my wishes.