I'd run this by Sakura8, she's dealt with velvet before.
I BELIEVE that aquarium salt can be used as a treatment, along with higher temps. Kosher salt can be used in place of aq salt, as well as ice cream salt.
You should be able to get your hands on one of those fairly cheaply. Even at walmart if not the pet store.
You want this http://www.petsmart.com/product/inde...Fish+Saltwater
or this one is available in smaller sizes, and dissolves quicker http://ca-en.hagen.com/Aquatic/Water...plements/A1091