I would keep the water conditions super clean to prevent any chance of bacterial infection. Perhaps you could try salt baths to help heal the wounds. I do salt dips, I have a quarantine tank to mix my salt bath in. 1 teaspoon of aquarium salt per gallon of water, I leave the betta in for 5 minutes then return it to the original tank. I usually treat them once for a wound caused by a plant etc just to prevent bacterial infections.
Make sure you dip water is the same temp as your tank water to prevent thermal shock to your betta. Use clean conditioned water for the salt dip, not water directly from the tank.
You should also remove your plastic plants from the tank to make sure you don't have fin rot on your hands rather then tearing from the plants. I would suggest a live plant, silk plants or non abrasive plastic plants for your new 5 gallon tank.
Last edited by JamieTron; 11-21-2009 at 11:34 PM.