Oh shoot... I used duramycin too this summer and I can't remember what I used.... I think I used 3 tsp. per quart. So I guess 12 tsp? I don't know how many table spoons that is. Maybe someone else can varify.
If 3 tsp per quart is correct, then it would be 1/4 cup per gallon. 3 tsp = 1 Tbsp 4 Tbsp = 1/4 cup Best check to make sure that is the correct dosage though.