Which size fits your well

For a big house on a well: seven or more people or four or more bathrooms. It does the same jobs as the 2.5 with 40% more carbon, so the carbon lasts longer in a busy house. The tank is 14 by 65 inches and stands about 69 inches tall, so check the ceiling height first. For high radon in a large family, Aidan sometimes puts two carbon tanks in a row; text him the number.

How to pick: on a well, the job decides first and the household second. For the taste or odor your other filters leave, size by people and bathrooms. For a light rotten egg smell or radon, start at the 2.5. For a chemical a lab test found (a solvent, fuel or PFAS), text Aidan the report at 443-277-2204: he sizes those from the numbers.

Why there is no GPM column

On city water we size by chloramine, which needs a set contact time per cubic foot of carbon. A well has no chloramine, so that number does not apply. More carbon means more contact time and a longer carbon life. We have measured peak flow only on the 2.5 (about 17 GPM); every size uses the same 1 inch Clack head and bypass, with no gravel bed. A non-backwashing tank also needs no backwash flow from your well, which matters on a weak pump Peak flow is what the tank passes wide open, not a treatment rating: radon and chemicals need contact time, which is why those jobs start at the 2.5.

What else a well needs with it

A 5 micron sediment filter ahead of it, if you do not have one (the 20 inch Big Blue sediment kit is $195), and a UV light after it only if your test shows bacteria. Budget a plumber's time on top.

Test before you buy

The standard well water test ($199) covers iron, hardness, pH, bacteria and nitrate, the problems that come first. Carbon's jobs have their own tests: the hydrogen sulfide test ($139) for a rotten egg smell, the radon in water test ($129), and the advanced well water test ($329), which adds 60 fuel and solvent chemicals.

On city water? The same tank is set up for chlorine and chloramine as the whole house water filter for city water; on city water it goes before the softener.

What ships

• Vortech 14x65 mineral tank, black, with a Vortech plate at the bottom that spreads the water evenly, so no gravel layer is needed. It ships empty.
• Clack C1190 non-electric in/out head with the Clack bypass valve, 1 inch PVC connectors, and the distributor tube, set up for upflow service. NSF/ANSI 44, 61 and 372 certified (Clack in/out head).
• 3.5 cubic feet of Centaur 12x40 catalytic carbon by Calgon Carbon, in three 1 cubic foot bags and one 1/2 cubic foot bag (3 x 1 cu ft bag, 1 x 1/2 cu ft bag). It is poured into the tank at install.
• Fill funnel for pouring the carbon in with the head off.
• Free shipping to the lower 48 states, by freight.

What does not ship

• 1 inch PVC connectors for the bypass are included; the fittings from them to your pipe are not.
• No drain line or electrical outlet is needed, so none is included.
• Install instructions: the manufacturers do not put any in the box. Use our whole house water filter install guide and Aidan's install videos, or text Aidan at 443-277-2204.

System

Centaur 12x40 (Calgon data sheet)

Reduces

Many VOCs (volatile organic chemicals such as solvents and fuel compounds) and some pesticides; the taste and odor left after an iron filter, acid neutralizer or softener; and, in the 2.5 and 3.5 sizes, a light rotten egg smell (under about 1 ppm of hydrogen sulfide) and radon. Activated carbon also reduces some PFAS. This tank is not certified for PFAS removal and we do not publish a removal percentage.

Does not remove

Carbon does not remove iron, manganese or hardness, does not raise a low pH, and does not remove bacteria, nitrate, fluoride or sediment; on a well those come first, each with its own filter. A strong rotten egg smell (above about 1 ppm) needs a sulfur filter: a carbon tank on strong sulfur helps for a few months, then runs out, and a used-up bed can put the smell back worse. A carbon bed can also grow bacteria, which is why a UV light goes after it, never before. It does not backwash, so on a well it needs a 5 micron sediment filter ahead of it.

Three ways to put carbon on a well, all sold here. Which one fits depends on what else is on the well.

Backwashing does not make carbon last longer, because carbon holds what it adsorbs; a backwash only rinses out dirt. So when a sediment filter and an iron filter are already ahead of it, a non-backwashing tank does the same job with no drain, no outlet and no water used. More in backwashing vs non-backwashing carbon filters.

Backwashing carbon tank, 2.5 cu ft | 20 inch Big Blue carbon kit

On city water? The same tank is set up for chlorine and chloramine as the whole house water filter for city water; on city water it goes before the softener.

Where it goes

On a well, the carbon tank goes last, after everything that takes out sediment, iron and hardness, and right before the UV light. That way it only handles what the other tanks leave behind. From where the water comes in:

1. The pressure tank.
2. A 5 micron sediment filter.
3. An iron filter or an acid neutralizer, if your test calls for them.
4. A water softener, if the water is hard.
5. This carbon tank.
6. A UV light, if your test shows bacteria. It goes after the carbon tank because it needs clear water, and because bacteria can grow in a carbon bed; the UV light treats them on the way out.

Keep it out of freezing temperatures and direct sun. If your outside spigots tee off before the treatment, irrigation water does not use up carbon. The full sequence is in the correct order for well water treatment.

The steps your plumber follows

1. Shut off the water and open a faucet to relieve pressure.
2. Stand the empty tank in place and tape over the top of the center tube, so no carbon falls into it. Carbon in the tube means no flow.
3. Pour the carbon in through the funnel, then add water just above the carbon so it starts soaking and pushing out its air.
4. Remove the tape and thread the Clack head onto the tank.
5. Connect the inlet and outlet with 1 inch fittings, following the flow arrows. The bypass labels are easy to misread; text Aidan a photo if you are unsure.
6. Leave the bypass in bypass and turn the water back on. Calgon recommends soaking Centaur for 12 hours, so the usual plan is that your plumber finishes here and you do the last step the next morning (about 15 minutes, no tools).
7. Open a cold tub faucet, turn this tank's bypass to service slowly, and bring it up slowly to full pressure. Run it until it runs clear, usually 10 to 15 minutes.

What to expect the first week

Black carbon fines on and off for two or three days are normal (Aidan, after refilling his own: "Saw black stuff on and off for like two or three days"). Run a tub or an outside spigot until it clears. Opening the water all at once is the usual cause of carbon in the valve.

The whole system, step by step: how to install a well water filtration system.

Between refills: nothing

No salt, no backwash, no settings and no annual service. Change the 5 micron sediment cartridge ahead of it on its own schedule.

When to refill

About 5 years in a typical home, 4 to 5 years on a light sulfur smell (Aidan); a bigger tank in the same house lasts longer. Carbon does not warn you when it is spent, and once it is exhausted it can release what it held, so refill on schedule rather than waiting for the taste or smell to come back. On a sulfur smell, the smell starting to return is the sign.

Refill: 3.5 cubic feet of Centaur: 3 x 1 cu ft bag and 1 x 1/2 cu ft bag. The 1 cubic foot bag is $295 today, so 3 x $295 = $885 plus the 1/2 bag, which Aidan prices by text. Take the head off and scoop or wet-vac the wet carbon out into heavy trash bags (a full tank is too heavy to tip), rinse the tank, pour in the new carbon, then soak and flush it the same way as the first fill. The tank and head are reused. If the carbon was treating radon, ask Aidan before you handle it: EPA notes that radioactivity collects on the carbon and the used carbon may need special disposal.

Centaur catalytic carbon refill

• Carbon filter for well water: when a well needs one
• The correct order for well water treatment
• Rotten egg smell in well water
• How to test for radon in well water
• Backwashing vs non-backwashing carbon filters
• Best whole house carbon filter
• How to install a well water filtration system
• The complete guide to well water filtration