I soak my Magnum 250 cartridge in about a 30-70 mix of bleach to water, for about 24 hours. It does an adequate job of cleaning it, not bleaching it. The idea, as I understand it, is for the bleach to disintegrate the organic matter in the filter, making it much easier to wash off. That it does very well. I still get about a week on a filter element before I have to change it.