I changed all HOB pads about twice a week to keep up with solid waste production. The HOB pads provide some biological filtration, but not much compare with live sand and rock in the tank as the pads are renewed twice a week. I do 75% WC weekly to reduce nitrate and remove dissolved organic compounds before they turn into nitrate. WC in fresh water does the job protein skimmer and deep sand denitrification do in Berlin reef system. My substrate is only 1/2" as any deeper will go anearobic.
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