What Is KDF 55?

KDF 55 is a high purity copper zinc alloy media (Kinetic Degradation Fluxion) used in water filters. Through a redox reaction it converts free chlorine into harmless chloride, reduces dissolved heavy metals such as lead and mercury, and helps control bacteria, algae and scale. It performs well in hot water, so it suits shower filters.

What is KDF 55?

KDF 55 is a water filtration medium made from a high purity alloy of copper and zinc, supplied as fine granules. KDF stands for Kinetic Degradation Fluxion, the name given to the redox process the alloy drives. The media was developed by KDF Fluid Treatment (now part of Kymera International) and is the copper zinc grade optimised for chlorinated municipal water.

Unlike activated carbon, which traps contaminants by adsorption, KDF 55 works chemically. The two dissimilar metals in the alloy form countless tiny galvanic cells. When water passes over them, electrons move between the metals and the dissolved contaminants, changing those contaminants into forms that are either harmless or easy to filter out. Because the reaction is electrochemical rather than physical, KDF 55 keeps working at temperatures that would degrade carbon, which is a large part of why it appears in shower filters.

How does the redox chemistry in KDF 55 work?

The core mechanism is oxidation reduction, usually shortened to redox. In a redox reaction one substance loses electrons (oxidation) while another gains them (reduction). The copper and zinc in KDF 55 sit at different points on the electrochemical scale, so placing them together in water sets up a continuous transfer of electrons.

With chlorine, this transfer converts free chlorine into chloride, a benign, water soluble ion that has no taste, smell or disinfecting harshness. This is a genuine chemical change, not simply the chlorine being held on a surface. For dissolved metals, the reaction plates or bonds the metal ions onto the media surface, so contaminants such as lead, mercury, nickel, chromium and copper are removed from the passing water. The same electrochemical environment is hostile to microorganisms, which gives KDF 55 its bacteriostatic property.

What KDF 55 reduces

• Free chlorine

  Redox converts free chlorine into chloride, a harmless water soluble ion, removing the harsh taste, smell and drying effect. Reduction stays high even in hot, fast shower flow.

• Water soluble heavy metals

  Dissolved metals such as lead, mercury, nickel, chromium and copper are plated onto the media by electron transfer, with industry data citing up to 98 percent reduction of these cations.

• Bacteria, algae and fungi

  The electrochemical surface is bacteriostatic, inhibiting microbial growth inside the cartridge and keeping the media bed cleaner between changes.

• Scale buildup

  KDF 55 helps prevent scale by disrupting how hardness minerals crystallise. Note it controls scale rather than removing limescale, and it does not soften water.

What does KDF 55 reduce in shower and drinking water?

KDF 55 is aimed at two main jobs: reducing free chlorine and reducing water soluble heavy metals. Industry figures put heavy metal reduction at up to 98 percent of dissolved cations under suitable conditions, while free chlorine reduction is high, typically well above 90 percent even at the fast flow rates found in a shower.

Beyond those two targets, the media helps control the biological and mineral nuisances that build up inside filters. Its bacteriostatic action inhibits bacteria, algae and fungi, keeping the cartridge cleaner for longer. It also helps prevent scale formation by interfering with how hardness minerals crystallise. It is important to be precise here: KDF 55 helps control scale, but it does not remove hardness and does not soften water. If you need softer water, that is a separate treatment.

Why does KDF 55 suit shower filters, and how does it pair with carbon?

Showers present a specific challenge. The water is hot and moving fast, and hot water strips more chlorine into the air as vapour, which is why chlorine smell is stronger in a shower than at the tap. Activated carbon, the other common filter media, becomes markedly less effective in hot water and can shed adsorbed contaminants back into the flow. KDF 55 has the opposite behaviour: the redox reaction is unaffected, and often more active, at shower temperatures.

For this reason many shower filters combine KDF 55 with carbon rather than choosing one or the other. KDF 55 handles the chlorine and heavy metal reduction reliably in the hot, fast flow and keeps the media bed clean, while the carbon captures some tastes, odours and organic compounds when conditions allow. The bacteriostatic action of KDF 55 also protects the carbon from bacterial fouling, which helps the carbon last longer at its point of use.

How is KDF 55 different from KDF 85?

KDF 55 and KDF 85 are both copper zinc redox media, but they are tuned for different water problems. KDF 55 is optimised for chlorinated water, so its strengths are reducing free chlorine and water soluble heavy metals. This is the grade you find in showers and in point of use drinking water systems fed by municipal supply.

KDF 85 is optimised for well water and groundwater. Its focus is reducing iron and hydrogen sulphide, the rotten egg smell common in untreated groundwater. It converts soluble iron into an insoluble form that can be flushed out by backwashing, and it turns hydrogen sulphide into an insoluble sulphide. Both grades also help control scale, bacteria and algae, but you choose the grade by matching it to the contaminant you are treating. For a chlorinated town supply feeding a shower, KDF 55 is the correct choice.

How to judge a KDF 55 shower filter

• Confirm the media is genuine KDF 55 copper zinc alloy, not an unnamed mineral blend
• Check whether it is paired with carbon for a broader reduction profile
• Look for reference to NSF/ANSI Standard 42 certification of the media
• Match the grade to your water: KDF 55 for chlorinated town supply, KDF 85 for well water
• Set realistic expectations: chlorine and metals are reduced, but hardness is not removed