This unique tab makes it easy to keep your spa water clean and clear with a special blend of chlorine and clarifier. Its erosion-style formula features dichlor and alum that quickly dissolves within minutes of applying it to the filter compartment. Simply add 1 tab per 600 gallons weekly to maintain a free chlorine level of 3-5 pp. These tabs are specifically designed for use in the filter compartment, with the added bonus of coating the filter cartridge and grabbing onto any pesky microscopic contaminants. Just be sure to regularly chemically clean the filter for optimal performance. However, these tabs are not recommended for use in non-traditional or bleachable spa surfaces.