If your Betta shows signs of Velvet, it is best to isolate him for treatment. If you are dealing with a Velvet outbreak in a fry tank, it is best to treat the entire tank. Do a complete water change if your betta is in his own container, and a 30-40% water change if it is in a community/fry tank and you must treat in the tank. Adding aquarium or rock salt (dissolve before introducing to the tank) will help until stronger medications can be purchased, and can be used in conjunction with medication. Many of the same medications that are useful in the treatment of Ick
are also good Velvet treatments. Aquarisol is my personal favorite medication for Velvet, but Maracide, Malachite Green, and Coppersafe (as well as other copper-based medications) can be used. Be aware that stong copper-based medications can eventually lead to poisoning, so water should be changed frequently after treatment to remove the medications, unless you are treating in a container that gets 100% water changes. Also be aware that some of these medications are harmful to plants and invertibrates, so do your homework before treating in tanks containing plants and invertibrates.
Once medications have been added, if at all possible, increase the tank temperature to 82-84 degrees F. This will speed the life cycle of Velvet and allow the medications to kill it faster. If your treatment container is too small to heat, allow the medications to work at their own rate but try to place the container in a warm area of the house. Keeping the tank dark will also help to destroy Velvet, as Velvet is actually a parasitic algae and requires a bit of light to survive. Keep an eye out for secondary opporunistic infections, as fish that contract Velvet are already in a weakened, vulnerable state.
Velvet Information and Symptoms @ petfish.net