xTool Smoke Purifier Replacement FilterA replacement filter set for your xTool Smoke Purifier. Suggestions on filter maintenance Pre Filter (replace after 7 15 days of use) Replace the pre filter when more than 70% of its surface is covered by dust that can't be removed. HEPA Filter (replace after 3 6 months of use) Replace the HEPA filter when it fails to filter out smoke. Main Filter (replace after 2 3 months of use) Clean the main filter when the dust on it causes poor suction of the