Please change the filter approximately every 500 hours of inhalation. This filter will keep the plates clean of positive charged ions and give you maintenance free operation. Failure to change this filter can void the warranty and give you diminished Hydrogen gas production. If you use your inhaler every day we recommend you change the filter every 6 months to make sure your filter is up to date. If you get a blue blinking light when you shut off the machine, this is indicating that changing the filter already is over due.