Your barbs should be fed once or twice a day but make sure you don't over-feed as left over food and the increased waste the fish will produce might harm your water quality as it rots in the tank. If your tank is new (less than 2 months old) and you didn't fishless cycle before adding fish, you need to make sure you feed as little as possible - just once a day and a small amount - until the tank is more mature and stable. Make sure you test your water regularly and keep up with water changes and gravel vacuums.