@ Mav3rick478,
Probably not much. As sponges are a 1000X faster than bacterioplankton at removing the labile DOC produced and they readily colonize dim and unlit areas everywhere in a system not a lot of surface area is going to be needed for a cryptic refugium. If you feel a canister filter would be better for your system than adding rubble or a section to your refugium I would think a 6" diameter canister would be more than adequate.
Probably not much. As sponges are a 1000X faster than bacterioplankton at removing the labile DOC produced and they readily colonize dim and unlit areas everywhere in a system not a lot of surface area is going to be needed for a cryptic refugium. If you feel a canister filter would be better for your system than adding rubble or a section to your refugium I would think a 6" diameter canister would be more than adequate.