Activated carbon and other filter media: what they are and how to handle them

Filter media is the loose material that sits inside a filter tank, housing or canister. Activated carbon is the most familiar kind, but gravel and a few other materials are used as well. Some systems are refilled rather than replaced whole, so you may be reading the label on a bag of media instead of the box of a cartridge. This guide explains the terms on that label, the two forms of carbon, what the layers in a tank are for, and how to buy, load, handle and store media. It does not say what any media removes from water, because that depends on your system and your water, and the maker's instructions are the place to look.

Granular carbon and carbon block in plain words

Granular carbon is loose grains. You pour it into a tank, a housing or a refillable canister, and the water flows through the spaces between the grains. Because it is loose, you buy it by weight or by the volume your instructions give, and you fill the container yourself.

A carbon block is carbon that has been bonded or pressed into one solid shape, usually a cylinder, and sold as a cartridge. Water is made to pass through the solid block rather than between loose grains. You do not pour or measure it. You replace the whole cartridge and check that it fits your housing, as described under Carbon Cartridges.

The two are not interchangeable. A system is designed for one or the other, and swapping would change how the water moves through it. If your system takes a cartridge, buy a cartridge; if it takes loose media, buy media. The word "activated" means the carbon has been processed so that each grain is full of tiny pores. You can browse the range under Activated Carbon.

What "coconut shell" and "mesh size" describe

Coconut shell tells you what the carbon was made from. Carbon can be made from several raw materials, such as coconut shell, coal or wood. The phrase names the source material. It is not a test result and it is not a promise about what the carbon will do in your system.

Mesh size describes the size of the grains. It comes from sieves: the grains are sorted through screens, and a label usually shows two numbers separated by an x, which give the range of screens the grains passed through and were held by. A higher mesh number means a finer, smaller grain. In general, smaller grains pack more tightly and slow the water more, while larger grains let it pass more easily. Which grade is right is a matter of system design, so use the grade your maker specifies, not the one that sounds finer.

Gravel and garnet: the layers under the media

Some media tanks are filled in layers. A support layer of gravel or garnet sits at the bottom, under the working media, and its general job is to support the media above it and keep it from being carried out of the tank with the water. Garnet is a dense, sand-like material. Whether your tank has a support layer, which material it uses, what grain size and how deep the layer should be are all decisions of the system design, and they are in the manual. Do not add or leave out a layer on your own.

Other media: use only what your system maker specifies

Besides carbon, you will see names such as calcite and KDF. These are media made for specific system designs. Whether any of them belongs in your system is the maker's decision, not yours, so use only what your system's instructions list, in the amount and order they give. You will find what the shop carries under Other Filter Media, and the Media & refills view collects it all in one place.

Buying by weight

Media is sold by weight, and tanks are sized by volume, so a little arithmetic helps. The instructions for your system should say how much of each layer the tank takes. Check whether that is given as a weight or as a volume. If it is a volume, remember that the same volume of gravel or garnet weighs far more than carbon, so do not assume one bag size fits every layer. Work out the amount before you order so that you are not guessing halfway through the fill. If you cannot find the quantity in the manual, ask the maker.

Loading and rinsing, step by step

Follow the maker's instructions, which always come first. The outline below is only a reminder of the usual order.

1. Turn off the water supply to the system and release the pressure as the instructions describe. Have towels and a bucket ready.
2. Open the tank or housing and remove the old media. Do not wash it down a drain, where it can block the pipes. Dispose of it as your local rules allow.
3. Rinse the new media if the instructions call for it. New media can carry fine dust, and many instructions ask for a rinse before use.
4. Add the layers in the order and depth the instructions give, support layer first, leaving the free space at the top that they call for. Use a funnel and pour slowly.
5. Close the tank, turn the water back on slowly and check for leaks.
6. Flush the system for the time or volume the instructions state before you use the water.
7. Write the date on the tank or in your calendar, and note when the maker says to refill.

Dust and handling sense

Dry carbon makes a fine black dust that spreads and stains. Pour it close to the opening, slowly, in a ventilated place or outdoors. Wear a dust mask, gloves and eye protection, avoid breathing the dust, and lay down a sheet or tray first. Spilled media of any kind can make a hard floor slippery, so sweep it up promptly. Keep opened bags away from children and pets. If you have a breathing condition, ask a health professional whether you should handle fine dust at all.

Storing media

Keep media in its sealed bag or container, in a dry place off the floor, and out of reach of children. Keep it away from paints, solvents, cleaning products and other strong-smelling things, because open carbon can pick up odors from the air. If you use only part of a bag, close it tightly again and mark the date. If a bag has been wet, smells musty or has torn, ask the maker before you use it.

Before you order

Write down the media and grade your system specifies and the amount each layer takes, then compare them with the product page for each bag. If you are replumbing at the same time, our guide to quick-connect fittings, tubing and valves covers sizes, threads and drip checks. If your question is about your water rather than your equipment, contact your local water utility (most publish an annual water quality report), a certified testing laboratory or a health professional.