SUStee is a ‘watering checker’ that can tell you when to water your plant by changing its colour. SUStee’s inner core is 100% natural, made from non-woven cotton, and can be easily replaced. Depending on the type of soil used, the inner core has a life span of 6 to 24 months. SUStee’s body is made from durable, high quality polycarbonate. A set of 2 inner core refills for SUStee Aquameter Large, which is suitable for pots larger than 18cm in diameter. The inner core of SUStee is made from non-woven cotton. Because of the bacteria in the soil the inner core corrodes over time and should be replaced every 6 to 24 months depending on the soil used. How do you know when to replace the inner core? Take the SUStee device out of the soil and verify the opening at the bottom. If the core refill has decomposed, it is time to replace it with a new one. It should also be replaced when the device stops reacting, even if the core refill is not entirely gone.