Keep your Lay-Z spa or pool clean and healthy with these filter cartridges. The filter cartridges are essential for Lay-Z spa and above ground pool pumps as they filter out dirt and grime from the water to help keep it clean and healthy. How do they work? They work by catching dirt and grime when the water is pumped through them. As your pump will usually be continuously cleaning and filtering the water when it is turned on, this dirt can quickly build up, especially when the hot tub/pool is regularly used.