1. Soak dulse in 1 cup of water for 20 to 30 minutes.
2. Bring approximately 2 quarts of water to boil. Quickly blanch the red onions, just until cooked through. Cool by immersing in cold water, and then drain.
3. Remove the dulse from soaking water and chop. You do not need the rich soaking water from the dulse, but it can feed your houseplants.
4. Mix vinegars and syrup with cucumbers, onions, and dulse.
5. Fold scallions and dill into the cucumber mixture.