The FROG @ease Test Strip Out Indicator on the back of the Test Strip Bottle indicates if the SmartChlor cartridge is empty:
When the test strip color is lighter than the single-color image on the bottle, it’s time to replace the SmartChlor Cartridge.
If you think the SmartChlor cartridge may be empty, remove it from the system, drain all the water and shake the cartridge. If you don’t hear any ingredients inside, it’s empty - it’s time to replace it. If not, put it back in and test the water again in a few days