Check out this TOPIC, which may help you out without repeating myself
Because it is a uniform loss of fin-age I would be tempted to say it has been bitten.
Do you know what he was kept with at the store?
How long have you had him?
Keep his water clean and add some IAL and hopefully it will start to heal.
Tell us some more about yourself. What size tank is your boy in, is it heated and filtered? Do you have any other fish/tanks?
Can you add your location to your profile as this assist with advising you due to different countries meds etc.