Eheim torf pellets consist of specially treated acidic peat. It is rich in valuable substances such as humic acids and trace elements (therefore do not wash it). Peat pellets lower (acidify) the ph value of the water and so reduce the water hardness. The pellets should however only be used if the ph value necessary for the particular type of fish is exceeded peat filtration is particularly suitable for tropical clear to black water. As a rule depending on the type of fish use when ph value is over 7.0. Freshwater use only. Replace every 3-6 weeks. Do not use with active carbon.