I have 12% food grade and do about 30 mls per ~10gal. Once every res change in a stinkbud system. When I did bubbleponics in single site 5 gal container, did 3% solution from store and did about 1-1/3 bottles per 5 gals per change. Both worked/working okay, they both demanded different amounts. Two different locations, using hardwater. Every grow unique in that sense.