Haven't treated for velvet before but when I treated for ick I premixed the salt in a 5 gallon bucket of tank water. I initially dosed at a ratio of 1 teaspoon salt per gallon, waited about 8 hours then dosed again to bring the ratio up to 2 teaspoons of salt per gallon. Did a water change about every 3 days replacing the amount of salt for only the replacement water. Continued this course of treatment for about 10 days with good success. Again, this was to treat ick. I've never had to treat for velvet so not sure if the treatment would be the same.