I usually dont have flat or squishy tires after using a CO2 cartridge, but I pump up the tires with a floor pump before every ride anyway.

If the tire does go flat after use on a ride, is it possible that something embedded in the tire is causing it, instead of the CO2? After all, the only reason to use one during a ride is if something is wrong with your tire and tube. Even if the tube is replaced, the problem still persists if something too small to be seen remains in your tire.

I had that happen once. After a succession of flats on one ride, close inspection at home revealed a tiny, tiny shard of a staple embedded in the tire.