Anyone have a small Primo water filter?

Don't have this filter, but IN GENERAL, filter media should be cleaned frequently. It seldom needs to be replaced, and this should be done carefully, to avoid removing all of your beneficial bacteria. If the filter media includes carbon, and you require the carbon to be active (ie, medicating, tannins removal), the carbon will wear out within 2-3 days , up to 2-3 weeks in a low load tank. So, if you don't need the carbon, or the media doesn't include carbon, just rinse away the solid wastes and keep using the same media. I use sponges until they literally won't work anymore--shrink beyond the needed size, or develop tears that allow water to go around the sponge.