If used as recommended, I have found this to be a great aid to keep spa water clean and clear with minimal chemicals used. It is imperative that you follow the recommended dosing schedule and change both the stick and water after 4 months. Pushing it past this gave horrible results. I use the DiChlor substitution method listed in the instructions and only dose with MPS upon startup and then once a week. I highy recommend this product if you follow the directions carefully.