Thickening 15D Filter Cotton for Mechanical and Biological Aquarium Filtration

Fish tank filter cotton is a core consumable for maintaining clean, healthy water in freshwater and marine aquariums. This 15D cotton pad is designed to capture suspended particles while providing a large surface area for beneficial bacteria to colonise, supporting both mechanical and biological filtration. Available in eight dimensions, it fits a wide range of internal filters, external canisters, and sump systems. The thickening construction allows it to hold more debris than thinner alternatives, reducing the frequency of replacements. One piece per pack, this filter cotton is a straightforward way to improve water clarity and reduce ammonia and nitrite spikes in your aquarium.

Features and Construction

This filter cotton is made from 15D polyester fibre, a fine-denier material that balances particle retention with water flow. Available in multiple sizes, it can be cut to shape or used as-is in most filter compartments.

Material and Build

The 15D cotton is a synthetic fibre that does not degrade quickly in water. It is soft enough to trap fine particles but dense enough to maintain its structure under normal water flow. The thickening design means it has more layers than standard thin pads, giving it greater dirt-holding capacity and a longer useful life between changes.

Size and Practical Fit

Eight sizes are offered: 120x30cm, 20x20cm, 20x30cm, 30x30cm, 30x40cm, 50x11cm, 50x40cm, and 60x40cm. These dimensions cover common filter compartments and can be trimmed with scissors for custom fits. The 50x11cm size suits narrow slots in many hang-on-back filters, while the larger 120x30cm roll is ideal for sump systems or large canisters.

Uses and Placement

Filter cotton is a staple in both freshwater and marine setups. It is typically placed after mechanical pre-filtration or as the first mechanical stage in a filter stack.

Event or Professional Use

For breeders, aquascapers, and commercial fish-keepers, the larger dimensions (120x30cm, 50x40cm, 60x40cm) allow high-volume filtration with fewer changes. The thickening construction handles higher waste loads, making it suitable for heavily stocked tanks or grow-out systems.

Everyday Home Use

For home aquarists, the smaller sizes (20x20cm, 20x30cm, 30x30cm, 30x40cm) fit standard internal filters and small canisters. Replacing the cotton every 2-4 weeks helps maintain crystal-clear water without expensive chemical additives.

Benefits and Buying Value

Regular filter cotton replacement is one of the simplest and most cost-effective ways to keep an aquarium healthy. This product offers a reliable material at a reasonable price per piece.

Reuse and Low Maintenance

Filter cotton is typically a single-use consumable, but its thick construction means it can hold more debris before needing replacement. Rinsing gently in dechlorinated water can extend its life by a few days, but replacement is recommended when flow slows noticeably.

Why Choose This Product

The 15D material is a proven choice for fine filtration without clogging too quickly. The availability of eight sizes means you can buy the exact fit for your filter, reducing waste and the need for cutting. One piece per pack keeps the purchase simple and cost-effective.