[Long-term Use]- each of them can maintain clarity for up to 4 months. We recommend replacing it every 3-4 months.[Natural SPA Experience]- The SPA mineral stick can automatically add trace minerals to the hot springs, reducing impurities in the hot springs to create clearer and cleaner water, making you feel as comfortable as you are in a pure spring [Durable Material]- Blue and yellow SPA mineral sticks are made of ABS. There are negative potential balls, negative ion activation balls, microcrystalline balls and alkaline tourmaline balls inside, they can bring you a natural and healthy SPA.[Easy to Use]- SPA mineral stick is easy to use, you just need to put it directly into the SPA filters or skimmers and let them do their work. Pls note: We recommend replacing it every 3-4 months.[Wide Application]- Our SPA in-Filter Mineral Sticks are suitable for filter that is longer than 7 inch and the diameter of the filter hole is larger than 1-1/4 inch, and they fit for SPAs and hot tubs up to 500 gallons / 2000L and pools to keep the algae out.Colour:yellow + blueMaterial:ABSPackage Contents:5 * SPA Mineral SticksOnly the above package content, other products are not included.Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.