Fluval U2 Aquarium Stage 2 Poly Carbon Cartridge (2 Pack)

I like this product because it fits perfectly in the canister, easy to use and it does what it promises!

I used it as a third internal filter. It's fine. I replace the filter mats every three weeks. As mentioned, only as an additional filter, or a helper filter for 200‑litre basins.

Price/performance top, happy to buy again...

These can be hard to find and expensive in stores. If you use it, make sure you're pointing the carbon end toward the inside, the white end going against the foam pad. If you do it backwards, you're clogging the carbon with detritus that would otherwise be caught by the white side.