RUSTGuard® - How often do I replace tablets?

Whink® RUSTGuard® prevents the formation of rust and hard water build-up in your toilet bowl and reservoir. 2 in 1 Hard water & rust toilet bowl cleaner. RUSTGuard contains no acids, caustics, chlorine bleach, phosphates or dyes and won't attack plumbing like chlorine bleach cleaners can.

RUSTGuard tablets should be replaced every 30 days. 

RUSTGuard tablets do visibly dissolve completely in the tank after a few days, but it convert to a gel that does remain for the duration.