The Mineral Reservoir is filled with minerals. Once they are wetted, the time-released mineral coating is effective up to 6 consecutive months or 1 pool season, whichever is shorter.
For winter climates where the season is only 4-5 months, once you remove the Mineral Reservoir from water for an extended period of time, it will not work again the following spring.
After that time, you will hear minerals inside and the cartridge will still feel full, however, the bacteria-fighting mineral is spent or depleted. What you hear inside is no longer effective to kill bacteria and must be replaced.
Every spring or every 6 months if your pool is open all year, replace your Mineral Reservoir and you’ll get the full FROG effect: