If you can cut a sponge to fit the space where the cartridge goes, you could put one into a Topfin but I would either buy a sponge filter or an AC filter that is designed to hold flexible media. The Topfin is not a flexible filter but is one that is designed to use EOM cartridges only. Most of the Topfin house brand seem to be downgraded versions of a Whisper or a Penguin filter. Because it is not flexible in media, I try to avoid them and use mostly sponge filters or canister filters. The few cartridge filters that I have are ones that I have chosen not to waste because they came free with something else I bought.