Chemically acting filter peat lowers the pH-value and reduces the water hardness.

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