I cleaned my litterboxes and filled them with fresh litter just over a week ago, and for the past few days I've noticed that even when the box is compeltely scooped out, there's a bad smell - I even tried taking the litter out of the boxes, cleaning them, and putting it back, and the smell is still bad. I have four cats and two boxes, so there's still quite a lot of litter left in both after only a week, so I really do not want to throw it all away and use fresh after only a week - it seems very wasteful, not to mention changing it once a week would be much too expensive. Has anyone else had this problem with WBCL? Those who use WBCL, how often do you need to replace the litter?