It depends on two things. First, if you are using hard water, this can cause lime build-up resulting in the disk degrading faster. We recommend the use of distilled water in all our incubators. Second, if you are setting and hatching regularly throughout the year, you will need to change your disk. Based on these two factors, we recommend changing your disk every 6 months to 1 year. Your disk is the white piece located inside your Humisonic units. You will receive one new disk already inside your Humisonic unit with your incubator purchase. Replacement disks are available in our store.