The Hydro-Logic Big Boy KDF85/Catalytic Carbon Upgrade Filter is a replacement carbon cartridge for the BIGboy dechlorinator that reduces chlorine, sulfur, iron, heavy metals, rust, and silt — the maker rates it to remove up to 99% of those contaminants at a flow of 7 GPM. It packs Granular Activated Catalytic Carbon with KDF85 media into a 20 in x 4.5 in cartridge, and the maker directs replacing it after 50,000 gallons filtered. This page gives the maker’s published specs, explains how a KDF85/catalytic carbon stage reduces chlorine and metals, and is honest about the specs the maker does not publish.
What it is
The Big Boy KDF85/Catalytic Carbon Upgrade Filter is the upgraded replacement carbon cartridge for Hydro-Logic’s BIGboy dechlorinator system. It uses Granular Activated Catalytic Carbon and KDF85 media in an opaque cartridge to reduce chlorine, sulfur, iron, heavy metals, rust, and silt. It carries maker part number HGC741626 and replaces the former HL 22070. This particular listing is the “4/CS” distributor pack code; what that code maps to as a purchasable unit is held (see Honest fit). It is a replacement filter cartridge — not the housing, the pump, or a reverse-osmosis membrane.
Guaranteed specifications
| Media | Granular Activated Catalytic Carbon with KDF85 media, opaque cartridge |
|---|---|
| Reduces | Chlorine, sulfur, iron, heavy metals, rust, and silt |
| Contaminant reduction | Up to 99% |
| Rated flow | 7 GPM |
| Replacement interval | After 50,000 gallons filtered |
| Dimensions (H x W) | 20 in x 4.5 in |
| Weight | 7 lbs |
| Part number | HGC741626 (replaces HL 22070) |
| Listing pack code | “4/CS” distributor pack code — the unit it maps to is held (see Honest fit) |
Why choose the Big Boy KDF85/Catalytic Carbon Upgrade Filter
- Catalytic carbon plus KDF85, not plain carbon. It pairs Granular Activated Catalytic Carbon with KDF85 media, a combination aimed at reducing not only chlorine but also sulfur, iron, and heavy metals that plain carbon handles poorly.
- High rated throughput. The maker rates it at 7 GPM, enough to feed a sizeable fill or a downstream reverse-osmosis stage without becoming the bottleneck.
- Long service interval. The maker directs replacement only after 50,000 gallons filtered, and describes the upgrade as offering twice the life of the Green Coconut Filter.
- A drop-in replacement part. It carries maker part number HGC741626 and replaces the former HL 22070, so it fits the BIGboy stage it was designed for without adaptation.
Best uses
- Dechlorination ahead of an RO membrane or reservoir fill. As the carbon stage, it strips chlorine and metals before water reaches an RO membrane or goes into a nutrient reservoir.
- Well water with iron and sulfur. The maker calls the filter great for well water, because the KDF85 media targets the iron, sulfur, and heavy metals common in well sources.
- BIGboy owners due for a media change. As the matched upgrade cartridge, it is the part to fit when the existing BIGboy carbon element is spent.
How KDF85 and catalytic carbon reduce chlorine and metals
A catalytic carbon cartridge works by two distinct chemistries. Catalytic carbon carries active sites on the carbon surface that catalyse the breakdown of free chlorine — and, more usefully, chloramine — into chloride, a reaction plain activated carbon drives far more slowly. Alongside it, KDF is a copper-zinc redox medium: it exchanges electrons with dissolved contaminants, converting free chlorine to chloride and driving some dissolved metals out of solution so they can be trapped, an oxidation-reduction mechanism distinct from ordinary adsorption. Together the two media reduce a broader set of contaminants than carbon alone, which is why this class of cartridge is used where source water carries iron, sulfur, or heavy metals rather than chlorine only. Because it is a chemical stage, it does not remove dissolved salts — that is the job of the reverse-osmosis membrane it protects — but by stripping chlorine first it keeps chlorine off an RO membrane, which chlorine would otherwise degrade.
Compatibility and care
- System fit: it is the upgraded replacement carbon cartridge for Hydro-Logic’s BIGboy dechlorinator, carrying part HGC741626, replacing HL 22070. Confirm your housing accepts a 20 in x 4.5 in cartridge before ordering.
- Flow: the maker rates the media at 7 GPM — hold flow within that rating so the water gets adequate contact time with the media.
- Replacement cadence: the maker directs replacing it after 50,000 gallons filtered — sooner on heavy chlorine or metal loads.
- Sediment first: pair it behind a sediment pre-filter so grit is caught before it reaches the carbon, extending the carbon stage’s useful life.
How it compares to a standard carbon cartridge
Carbon cartridges differ in the media they pack and the contaminants they target. This table is factual — it does not claim this filter out-performs any other; which fits your housing and water is an operator’s decision.
| Factor | Big Boy KDF85/Catalytic Carbon (this filter) | Standard granular activated carbon cartridge |
|---|---|---|
| Media | Granular Activated Catalytic Carbon + KDF85 | Plain granular activated carbon |
| Targets | Chlorine, sulfur, iron, heavy metals, rust, and silt | Mainly chlorine and taste/odour |
| Rated flow | 7 GPM | Varies by cartridge — check the maker rating |
| Replacement interval | After 50,000 gallons | Varies; often shorter for equal media volume |
Where it fits
For more water treatment and filtration gear, browse the filtration & RO units category. This carbon stage sits in the middle of a filtration train and pairs with the parts around it:
- Hydro-Logic Big Boy KDF85 Catalytic Carbon Filter — the standard BIGboy carbon cartridge listing for the same filtration stage.
- Hydro-Logic Micro 75 GPD Reverse Osmosis System — a compact RO unit the dechlorination stage protects downstream.
- Hydro-Logic GroGreen Garden Hose Filter — an inline hose filter for lighter-duty sediment and chlorine reduction.
- Hydro-Logic FlowMaster Ultra Low Flow Model — a flow-control accessory for the RO stage behind this filter.
Frequently asked questions
What does it remove? The maker says it reduces chlorine, sulfur, iron, heavy metals, rust, and silt, up to 99%.
How often do I replace it? The maker directs replacement after 50,000 gallons filtered.
What are its dimensions? 20 in x 4.5 in (H x W), weighing 7 lbs.
What is the part number? It carries HGC741626 and replaces the former HL 22070.
What micron rating is it? The maker does not publish a micron rating for this cartridge on its product page, so it is not stated here (see Honest fit).
Who this is for — and who should skip it
Suited: growers running a Hydro-Logic BIGboy dechlorinator who need the matched upgraded Granular Activated Catalytic Carbon / KDF85 cartridge, especially on well water carrying iron, sulfur, or heavy metals rather than chlorine alone.
Not for / its limits: this is a replacement filter cartridge — not a housing, a pump, or an RO membrane, and it does not purify water on its own. It is a chemical dechlorination/metal-reduction stage; it does not remove dissolved salts, which is the RO membrane’s job. Confirm your housing accepts the 20 in x 4.5 in size before ordering.
HELD (not stated because not sourced): the maker’s product page does not publish this cartridge’s micron rating, its maximum-pressure rating, a chloramine-specific reduction figure (the page lists chlorine, not chloramine), or any third-party certification — none are stated here. The distributor “4/CS” pack code appears in this listing’s title; what it maps to as a purchasable unit is not something the maker publishes, so its interpretation is held. The live retail price is the storefront price field at deploy, not set or guaranteed here; any warranty term is held per store policy and not reproduced.
Ready to refresh your dechlorination stage? Add to cart, or talk to a grower about matching this cartridge to your BIGboy housing.
Sources
- Hydro-Logic (HydroLogic Purification Systems) — manufacturer product page for the BIGboy KDF85/Catalytic Carbon Filter (reduces up to 99% of chlorine, sulfur, iron, heavy metals, rust and silt; rated at 7 GPM; twice the life of the Green Coconut Filter; great for well water; replace after 50,000 gallons filtered; replaces HL 22070; Granular Activated Catalytic Carbon, KDF85 media, opaque cartridge; dimensions H x W 20″ x 4.5″; weight 7 lbs; part number HGC741626; HTTP 200, retrieved 2026-07-08 via WAF-immune fetch): https://www.hydrologicsystems.com/products/kdf85catalytic-carbon-upgrade-filter-20×45-for-big-boy
- General catalytic-carbon and KDF (copper-zinc redox) reduction chemistry (universal, physics-definitional): catalytic carbon catalyses the breakdown of chlorine and chloramine to chloride at the carbon surface, while a redox medium exchanges electrons with dissolved contaminants to convert chlorine and precipitate some metals — a mechanism distinct from ordinary adsorption. No product-specific value is drawn from this general chemistry.
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