Filox vs Katalox Light: Which Iron Filter Media Is Better?
Number copied. Text it from your phone: 443-277-2204.
Filox and Katalox Light are both made to take iron, manganese and rotten egg smell out of well water. Filox weighs 114 lb per cubic foot against 66 for Katalox Light, and that weight changes how much water your well has to push through the tank to backwash it.
Every iron filter we sell uses Katalox Light, so I am not a neutral judge. That is why this page works from each maker's own sheet, shows the math, and tells you where Filox still makes sense.
Quick Answer
Filox is a manganese dioxide iron filter media, similar to Pyrolox and Pro-OX, that Watts sells as Filox-R to remove iron, manganese and hydrogen sulfide. Watts' sheet asks for 16 to 30 gallons a minute per square foot of tank to backwash it, and Watch Water's sheet asks 10 to 12 for Katalox Light. For most wells, Katalox Light is the better choice, because the flow your well can supply is what decides it.
- What Filox is. Watts' own numbers for pH, iron and weight. See what Filox is.
- Backwash flow. What each media wants on our four tank sizes. See backwash flow by tank size.
- Chlorine or air. Watts recommends an oxidizer ahead of Filox. See what Filox needs ahead of it.
- Already have Filox. Keep it or switch. See switching to Katalox Light.
We sell Katalox Light only, in our iron filters from $2,495 and by the cubic foot at $325 for a tank you already have.
What's in This Guide
What is Filox?
Filox is the name of an iron filter media that Watts sells as Filox-R, made of 75 to 85% manganese dioxide. Watts says it takes out iron, hydrogen sulfide and manganese. Its sheet lists 10 ppm of iron, 3 ppm of hydrogen sulfide and 5 ppm of manganese, a working pH of 6.5 to 9.0, and a bed at least 20 inches deep.
It is heavy, 114 lb per cubic foot, and a half cubic foot bag weighs 57 lb. Katalox Light is built differently: a zeolite base with a 10% manganese dioxide coating, 66 lb per cubic foot, made in Germany by Watch Water. Pyrolox and Pro-OX are other makers' manganese dioxide media with their own sheets; they are covered in how the media compare, and we sell none of them.
Filox vs Katalox Light side by side
Here is each one on its own maker's sheet: Watts for Filox-R, Watch Water for Katalox Light.
| Filox-R (Watts) | Katalox Light (Watch Water) | |
|---|---|---|
| What it is | 75 to 85% manganese dioxide | A zeolite base with a 10% manganese dioxide coating |
| Weight per cubic foot | 114 lb | 66 lb |
| Backwash flow, gallons a minute per square foot of tank | 16 to 30 on the sheet (12 to 15 on an older copy of the sheet) | 10 to 12 |
| pH on the sheet | 6.5 to 9.0 | 5.8 to 10.5 |
| Chemical or air | An oxidizer ahead is recommended; 4 ppm free chlorine is the limit | No mandatory dosing |
| Iron, manganese, hydrogen sulfide | 10 ppm, 5 ppm, 3 ppm | Our filters: up to 30 ppm, 15 ppm, 10 ppm |
| How long it lasts | No years printed | 7 to 10 years (I tell customers 6 to 8) |
The iron, manganese and sulfur row compares two kinds of number. Watts prints what the media removes; ours are the ratings of our filters on the water coming in. An older copy of Watts' sheet, still on distributor sites, prints pH 5.0 to 9.0 and 15 ppm of iron. Watts' current sheet says pH 6.5 and 10 ppm.
How much backwash flow does each need?
Backwash is the reverse flow that lifts and cleans the bed. A heavier media takes more water to do it, and the sheets put a number on it: 16 to 30 gallons a minute per square foot of tank for Filox, 10 to 12 for Katalox Light. Watts asks for the bed to rise at least 15% in the backwash. Multiply by the area of your tank and you have what your well has to supply.
Take our 2.5 cubic foot filter, a 13-inch tank with 0.92 square feet of bed. Katalox Light wants 9 to 11 gallons a minute. Filox, on Watts' sheet, wants 15 to 28. Watts disagrees with itself here: the older copy of the sheet says 12 to 15, which makes the same tank 11 to 14. Either way, Filox asks for more water than Katalox Light on every size.
The flow each of our filters is set to use is in the table on how an iron filter works, and the sizing guide shows how to measure your well with a bucket. A caller had about 9 gallons a minute and asked about the 2.5 cubic foot. I told him it would work if the backwash ran 20 minutes instead of 10.
Does Filox need chlorine or air?
Watts recommends feeding an oxidizer into the water ahead of Filox: oxygen, chlorine, ozone, hydrogen peroxide or potassium permanganate. Its sheet says oxidizers help Filox work quicker and keep cleaner, and it caps free chlorine at 4 ppm or the bed can be damaged.
The sheet also gives a screening test. On a calibrated ORP meter, a reading above negative 170 millivolts means Filox can possibly work without an extra oxidizer, and a reading below it means you need one. Katalox Light has no mandatory dosing, says Watch Water. Our filters add an air pocket in the same tank, and without the air the Katalox Light still removes up to 30 ppm of iron; the air helps. Chlorine does not hurt Katalox Light. I told a caller it can help.
Which one fits my well?
For most wells, Katalox Light is the better choice, because it asks for less backwash water and needs no oxidizer to be fed. Filox is a real option when your well can supply what Watts' sheet asks and you can add an oxidizer ahead of it.
| Your well and water | What the sheets point to |
|---|---|
| A modest flow from the well | Katalox Light. Filox asks for more water on every tank size. |
| Plenty of flow, and you can feed an oxidizer | Check each sheet's full conditions; on flow and oxidizer, either can fit. |
| pH under 6.5 | Filox's sheet starts at 6.5 and Katalox Light's at 5.8, so check each sheet and raise the pH if needed. I want ours near 8. |
| Rotten egg smell with the iron | Both list hydrogen sulfide: 3 ppm for Filox, up to 10 ppm in our filters. |
In the video I go through the media we have tried over the years, and I say Pyrox, Phylox, Birm and greensand "all do a decent job up to a certain point, but they don't perform like Katalox Light."
Send me your numbers
Text a photo of your lab report and tell me how many gallons a minute your well delivers. I will tell you which media and size fit.
8 AM to 5 PM Eastern, seven days a week. A real person, not a call center.Can I switch from Filox to Katalox Light?
Katalox Light can go into a tank that had another media, but it depends on the valve and the tank. In the video I put it plainly: "you can do that, but it depends." Katalox Light does best with a valve that has a strong backwash and a tank that spins the water up through the bed, and in some tanks it may or may not work. It needs a Fleck 2510-class backwashing valve, and it is too dense for a Fleck 5600.
What a media change takes, and the other-brand-tank question in full, are in what Katalox Light is. By the cubic foot it is $325. If your pH is low, say 5.5, I say in the video a backwashing acid neutralizer goes in front first, because we want the water near 8 to remove iron, sulfur and manganese properly.
What buyers wrote about Katalox Light
These are verified purchases from our Stamped reviews, newest first. None of them compares Filox; they show what Katalox Light did on their water.
| Buyer | Bought | What they wrote |
|---|---|---|
| Lav A., Aug 2026 Verified buyer | Fleck 2510AIO 1.0 cu ft iron filter | "My iron level was 7 PPM. I bought a 1 cu. ft. iron filter media from Mid-Atlantic Water and installed it myself. It works great, no more red stains in the toilets." |
| Amy H., Oct 2024 Verified buyer | Two 2.5 cu ft iron filters | "I have well water with over 20 ppm ferrous and 7 ppm of ferric iron, along with manganese and some sulfur. ... Wow...and now the tanks reduced the iron to literally zero!" |
| Dustin H., Jun 2024 Verified buyer | 2.5 cu ft iron filter | "I am on a well with mildly acidic water around 6.5 with ferrous iron in it ... Cleaned out the iron and raised the ph to 7.5." |
Frequently asked questions
What is the best filter media for iron removal in water treatment?
It depends on your water, and each maker's sheet gives its own conditions. For most wells I use Katalox Light, which is in every iron filter we sell. Birm, greensand, Pyrolox and Pro-OX are compared in how the media compare.
Do air injection iron filters work?
Ours does. The air pocket and the Katalox Light share one tank, and without the air the Katalox Light still removes up to 30 ppm of iron; the air makes it more effective. The valve backwashes every day, which refills the air pocket. The steps are in how an iron filter works.
How often do you need to change an iron filter?
Ours has no annual service. The Katalox Light itself is changed about every 6 to 8 years, depending on your water use. The media change step by step is in iron filter maintenance.
What is the best iron filter on the market?
I can only speak for what I have used. In 32 years we have tried every different type of iron filter media, and the one I stand behind is Katalox Light in an air injection filter, where the air pocket and the media share one tank. Our four sizes run from $2,495 to $3,495, and the size follows your household and your well's flow.
Aidan Walsh
Co-owner & Residential Water Treatment Specialist, Mid Atlantic WaterAidan Walsh has spent 32 years in residential water treatment, the first stretch of it installing and servicing well systems before Mid Atlantic Water became an online supplier. Mid Atlantic Water is a family company; every recommendation on this site is based on what actually failed in the field and what fixed it. If you have a question this page did not answer, call 800-460-5810 or text him at 443-277-2204.
Aidan answers calls and texts 8 AM to 5 PM Eastern, every day.Number copied. Text it from your phone: 443-277-2204.