Thank you for your question, izoid. Matrix will work well in almost any capacity, and it does not have to be used in a canister filter. In fact, in our large systems here at Seachem, we just place it directly into the sump, as there is very little maintenance required, and Matrix never requires replacing. Because you will most likely be changing/cleaning your filter sock regularly, I might suggest placing the Matrix elsewhere in your sump, but this is completely up to you, as it will house beneficial bacteria wherever you may choose to place the media. Hope this helps!