Weco Fine Mesh Zipper Media Bag (4 x 8 in) | Reusable Filter Bag for GFO, Resin & Fine Carbon

The Weco Fine Mesh Zipper Media Bag is the bag you grab for fine and powdery media — GFO, ultra-fine carbon, purifying resin, or any granular media that would slip through a coarse weave. The tight ~420-micron mesh holds the smallest grains in place while still letting water flow, and the full-length zipper keeps everything sealed even after a year of rinsing. Browse our full filter media & cartridges or shop maintenance & water care.

What It's For

This is the bag for fine, powdery, or small-granule media — Granular Ferric Oxide (GFO), ultra-fine activated carbon, phosphate-removing resin, nitrate-reducing resin, polishing resin, and similar small-particle filtration media. If you're running chunky media like ceramic rings, bio-balls, or pelletized carbon, grab the coarse mesh version instead — the fine weave creates more flow resistance than chunky media needs.

Features

How to Use

Fill the bag with your chosen media — for GFO and similar dense media, ½ to 1 cup is typical for a 4 × 8 bag. Zip it fully closed and rinse the bag under fresh water to flush any dust before placing it in your sump, canister tray, or HOB media basket. Position it where water flows through the bag rather than around it. Rinse the media every 2–4 weeks for GFO or as directed for other media. Replace the media on its own schedule and reuse the bag.

Specifications

Recommended Media to Pair With

• Red Sea REEF-SPEC Carbon — fine carbon for reef tanks
• Aquaforest AF Purifying Resin — freshwater nitrate-reducing resin
• Aquaforest AF Carbon Freshwater — granular carbon for FW
• Brightwell Purit — chemical filtration media
• Browse the full filter media collection

FAQ

Fine or coarse — which do I need?
Fine is for powdery or small-granule media (GFO, ultra-fine carbon, polishing resin). Coarse is for chunky media (carbon pellets, ceramic rings, bio-balls). If the media looks like sand, salt, or powder — go fine. If you can see individual chunks — go coarse.

How often should I rinse?
For GFO and dense reactor media, rinse every 2–4 weeks to clear gunk and keep flow rates up. For polishing resin or fine carbon, rinse monthly. The bag itself rarely needs replacing — just the media inside.

Is the nylon safe for reef tanks?
Yes — inert nylon mesh is reef-safe and won't leach anything into the water column. Rinse before first use to clear manufacturing dust.

Will GFO leak through the fine mesh?
No — the ~420-micron weave is tight enough to hold standard GFO granules. Rinse the GFO well before bagging it to wash out the dust, then load into the bag and zip closed.