Carbon can be used if you want but it isn't necessary unless you have lots of chemicals in your water supply. Then the carbon will help to remove them from the water. However, most water supplies are not that bad.
Many people use carbon after they have treated their tank for a disease but don't use it at other times. Doing bigger and more frequent water changes will help to reduce the medication in the water and will also help reduce the fishy smell you have. You should also do a gravel clean and suck out any uneaten food once the fish have been fed. Rotting food is the biggest cause of smelly tanks.