Description
This 20″ Slow Phos filter cartridge (4.5″ x 20″) helps stop limescale before it builds up inside your water heater, ice machine, coffee equipment, and pipes. It fits any standard 20″ Big Blue housing, so there’s nothing to modify. Just drop it in.
How a Slow Phos Cartridge Works
The cartridge is packed with food-grade polyphosphate beads that dissolve slowly into the water passing through. The phosphate keeps hardness minerals from clumping together and sticking to hot surfaces, which is how scale starts. It also lays down a very thin protective film on metal pipe walls, which helps guard against corrosion.
Hard water is the norm in much of the country, and any appliance that heats or boils water will scale up over time. Left alone, scale shows up as white crust on faucets and shower heads, spotted glassware, stained fixtures, and less efficient equipment.
What It Handles, and What It Doesn’t
- Scale: keeps hardness minerals from forming deposits when water is heated. Maximum hardness: 15 GPG.
- Corrosion: helps protect metal surfaces from the effects of water chemistry. Recommended pH range: 6.5 – 9.0.
- Iron: holds dissolved iron up to 1 ppm in suspension so it doesn’t stain.
One honest limit: polyphosphate controls scale, but it doesn’t soften water or remove minerals. If your hardness is above 15 GPG, or you want softer water for bathing and laundry, you’ll need a water softener as well.
Where to Use It
Install it on the line feeding equipment that heats or boils water, including tank and tankless water heaters, ice machines, coffee and vending machines, food service equipment, and air conditioning equipment.
When to Change It
Replace the cartridge every 4–6 months. Go by the calendar rather than by taste. Scale protection can fade well before you notice any change in how the water tastes, so waiting for a taste change means running unprotected for a while.
Specifications
| Feature | Details |
|---|---|
| Cartridge Size | 4.5″ x 20″ (Big Blue) |
| Media | Slow-melt food-grade polyphosphate beads |
| Construction | ABS cap and body, PE pad, TPE gasket, sonic welded |
| Micron Rating | 25 |
| Flow Rate | 5 GPM |
| Pressure Range | 20 – 125 PSI |
| Temperature Range | 40 – 90 °F |
| Maximum Hardness | 15 GPG |
| pH Range | 6.5 – 9.0 |
| Iron Sequestered | Up to 1 ppm |
| Change Interval | Every 4–6 months |
| Certification | Phosphate listed under NSF/ANSI 61; FDA-grade materials |
| Origin | Made in the USA |
20″ or 10″?
| Cartridge | Fits |
|---|---|
| 20″ Slow Phos (this cartridge) | Standard 4.5″ x 20″ Big Blue housings. More phosphate media per cartridge. |
| 10″ Slow Phos | Standard 4.5″ x 10″ Big Blue housings. |
Need a housing for it? See our Big Blue filter systems. If your water carries sand or rust, add a sediment pre-filter ahead of this cartridge so the phosphate beads stay clear.
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