Works fairly well, at least my green algae is under control but not completely gone (reason for 4 stars), even with all other chemicals balanced and also using algaecide. Each 3-liter bottle comes with a small test tube and about a dozen tablets for determining amount of phosphates in your pool. I was hoping though that it would last longer since it's supposed to stay in the filter until, I guess, back-washed out. Getting it through Amazon is by far the cheapest place. I also tried to find the main ingredient, Lanthanam, separately in bulk through a chemical supply warehouse but no such luck yet. Anyway, I guess it's all part of having a pool.