Improves water clarity in just a few hours! Place one cube in the pump basket, not the skimmer basket, leave the filter running untill water becomes clear – usually within 24 hours, then backwash and rinse. it’s as easy as that! And it keeps working for up to 3 weeks. 2 Boxes, 4 Cubes per box. Use one cube for pools up to 12,500 gallons.