If you want a carpet, then you should keep them in a species tank. Many carpets are known to eat fish and inverts. Only safe if is a handful of different species of clownfish.
Depending on the type of carpet you have, you will need either a very deep sand bed or just regular live rocks.
Many carpets being sold in LFS are usually not doing well. You will have to risk buying one and hoping you will be able to nurse one back to health if its unhealthy.