Foam Round Xlarge. Ensure a healthy and clean aquarium with this Foam Round XLarge filter. This highly effective aquarium filter foam provides superior mechanical and biological filtration, trapping large debris and providing a massive surface area for beneficial bacteria to colonize. Its extra-large, round design makes it a versatile replacement filter media that can be cut to fit a variety of filter systems, helping to keep your water crystal clear and your aquatic life healthy. This durable bio-sponge is also reusable, making it a cost-effective choice for long-term aquarium maintenance.