scoop free litter formula change?

[davmar77]

we've had this automatic littler box for a few years. we just replaced our old dying unit. we had two cats but sadly lost one a short while back. i recently noticed the litter seems to require changing more often than when we first started using it. with two cats i think we got at least a month or more out of a cartridge. now with one cat it seems to need replacing after only about 3 weeks. does anyone know if the formula has changed? of course this would make more money for the manufacturer if you have to buy 30% more cartridges. i think the box recommends changing it about this often but i don't recall if it was always that way. does anyone know a better cartridge that fits this unit or a way to extend it's use? it's really the smell that's the issue. maybe there's an additive to the litter to help. we've tried various room deodorizers but none seem to work as well as advertised.
thanks,
dave