There are no filters on the Hydro-Gear EZT hydros. The fluid can be changed however, the hydros must be removed from the machine, the fill port bolt must be removed and the hydros must be dumped. It’s possible to use a fluid extractor without removing the hydros. Refill with 20W50 engine oil or Mobil 1 15W50. The link below will explain everything that you need to know.