I use Dharma Trading fiber reactive procion dyes. Here are the quantities I use--instructions on are their website:
2 gallons of water for up to 2 yards of pre-washed fabric
1 lb non-iodized salt
1/8 teaspoon dye dissolved in water
1/2 cup soda ash
Every time I've used 1/4 teaspoon I've been unsatisfied with the result.