This micro clean filter complies Unicel # AK-2392, Filbur # FC-2392 and OEM # FC-2392 specifications. It is so hassle free that you don’t need to check filter for 2 months after placing it in spa. As per the use, the filter changes its color from outside to inside. Almost after two months if you don’t find any white space on the filter, it is time to replace it. Expansion of the filter material is normal as it absorbs and removes debris - filtration improves as it expands. Do not use defoamers, clarifiers, cleaners, enzymes, stain and scale mineral removers or descummer chemicals. These chemicals are not necessary with Micron filters and will reduce the life of the filter because the filter will absorb these oils. If you have been using these chemicals in your water, drain your water before switching to Micron disposable filters.