Buy the bucket, good for 150 gallons, just once. Once consumed, fill it up with three of the 4 bags from the boxed salt. Make sure to seal the bucket well after each use. When the bucket is almost empty, empty the last bag into the bucket and order the next box. Works for me, and I've been doing it this way for almost 3 years, one box of 4 bags good for 200 gallons lasting me about 6 weeks at a time.