My LFS store has told me that I should change Eheim EhifiMech and
EhfiSubstrat every 8 months. When I asked the reason. I was told that after
a while 'bad' bacteria builds up and it becomes ineffective. If this is the
case, could I boil it (and thereby remove any impurities) and use it again?

TIA - Dave

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cadasco at hotmail dot com
Hampshire - UK