At least twice a month. Check it for cracks, or tears in the element, and for color. The filter's natural color is white so if you see that it is a light gray color, you may just need to clean the filter. Your Diamante Spas dealer can advise you with a good cleaning method. If the filter is a dark gray or even black in color, you may still be able to clean it, but if the cleaning does not work then you will need to replace it. Your Diamante Spas dealer has replacement filters in stock for you.