2-Stage Whole House Water Filtration System — 3/4″ Port, Solid Blue

Also labeled as: MWC-DUAL-B34 — same system, same filters and parts.

This page covers specifications, installation, routine filter changes, and the exact replacement parts that fit this model.

Count your housings and check their width before ordering — these are the two things that decide which cartridges fit.

• Two slim housings (this system) — takes a 2-cartridge set, 10″ × 2.5″.
• Three slim housings — that’s a 3-stage system and needs a 3-cartridge set. Find your model →
• Wide housings (~4.5″) with 1″ ports — that’s a Big Blue system and takes entirely different cartridges. Find your model →

Mounting, plumbing connections, startup, and the filter-change procedure.

Open the manual →

This system doesn’t include built-in shutoffs. A ball valve on the inlet and the outlet lets you isolate the unit for filter changes without shutting off water to the whole house — it turns a 20-minute job into a 5-minute one. If your installer didn’t fit them, you’ll need to close your main house shutoff before every change. Valves and union nipples are in the parts section below.

Component	Typical interval	Change sooner if…
Both cartridges Change as a complete set	3–6 months	Water pressure drops · taste or odor returns · visible discoloration · heavy sediment or well water
Housing O-rings	Inspect every change Replace every 12–24 months	Cracked, flattened, brittle, or weeping at the seam
Filter housings	3–4 years	Any crazing, hairline cracks, cloudiness, or a leak that a new O-ring doesn’t stop

Filter housings are under constant line pressure. Over years the plastic fatigues and can crack without warning — a failed housing on a main line can flood a home.

Replace both housings on this system every 3–4 years regardless of appearance, and immediately at any sign of crazing, cracking, or a persistent leak. Write your install date on each housing with a marker, or on the magnet, so the next change is easy to date.

The like-for-like replacement. Your system was built around the coconut-shell block in Stage 2 — denser media, longer carbon life, cleaner taste.

Whatever you swap, Stage 1 stays a sediment cartridge — it protects the stage behind it. Specialty media go in Stage 2, in place of the carbon block. With only two housings you have one specialty slot, so pick the media that matches your biggest water problem.

Cartridge	Best for	What it does
Stage 1 — Sediment
Pleated Sediment — Washable SED5-PLT · 5 µm	Heavy sediment & well water	Traps dirt, silt, sand, and rust like the standard sediment filter, but the pleated construction can be rinsed and reused instead of replaced. Worth the swap if Stage 1 is loading up faster than your carbon stage.
Stage 2 — carbon options
Coconut Shell Carbon Block HQCBC-10-5 · 5 µm	Everyday chlorine, taste & odor	This is the same media your system shipped with, sold as a single cartridge. Coconut-shell block at 5 micron — reduces chlorine, the tastes and odors it causes, and many VOCs, while polishing out fine particles. Buy this if you only need to replace Stage 2.
Advanced Catalytic Carbon CAT-10 · GAC-style	Chloraminated city water	Catalytic carbon. Standard carbon block has limited effect on chloramine — this is the correct swap if your utility disinfects with chloramine rather than free chlorine. Also helps with hydrogen sulfide (rotten-egg smell). Check your utility’s annual water report if you’re unsure which they use.
Premium Catalytic + KDF-85 CATKDF85 · 3/4 lb KDF	Chloramine + H₂S + metals · longest life	Catalytic carbon blended with KDF-85. Covers what the catalytic cartridge does and adds heavy-metal reduction. The KDF component also inhibits bacterial growth in the media bed, so it typically runs longest of the carbon options. The most capable Stage 2 in the slim range.
Stage 2 — targeted water problems
Iron Reduction — Iron-Removal Resin IRON10	Clear-water iron staining	Iron-removal resin that reduces dissolved iron — the usual fix for orange staining in sinks, tubs, and laundry on well water. For clear-water (dissolved) iron only. If your water comes out of the tap already orange or rusty, the iron has oxidized and needs a backwashing iron system instead. A supporting stage, not a whole-house iron filter.
Scale & Corrosion Inhibitor SCALE10 · polyphosphate	Limescale & corrosion protection	Polyphosphate media that holds hardness minerals in suspension so they’re less able to form scale in pipes, water heaters, and appliances, and helps limit corrosion of metal plumbing. Important: this does not remove hardness minerals and is not a water softener. Your water will still test hard and still feel hard — the benefit is protecting your plumbing, not soft water.

The right swap depends on what’s actually in your water, and more than one of these can be the wrong answer for a given problem. A water test is the reliable way to choose — guessing usually costs more than testing.

Browse all 10″×2.5″ specialty cartridges →  ·
Send us your water report →  ·
Free basic testing in San Diego →

What you’re seeing	Most likely cause
Water pressure has dropped through the house	A loaded sediment cartridge in Stage 1. This is the normal end-of-life signal — change the set.
Leak where the housing meets the cap	O-ring not seated in its groove, or worn. Depressurize, reseat or replace the O-ring, lightly grease it.
I have to shut off the whole house to change filters	This model ships without built-in shutoffs. Adding a ball valve on each side makes future changes much faster — see the parts section.
Grey or cloudy water after a filter change	Carbon fines and trapped air. Normal. Flush a cold tap for 5–10 minutes.
Chlorine taste or smell has come back	Stage 2 is exhausted. Change the set. If your utility uses chloramine rather than chlorine, standard carbon has limited effect — swap Stage 2 for a catalytic cartridge.
Housing won’t unscrew	Line pressure still in the housing, or it was overtightened last time. Confirm the water is off and pressure released, then use the long-reach wrench.
I ordered a set and got three cartridges	That’s a 3-stage set. This system takes a 2-cartridge set — check the stage count before ordering.
Water is still hard, or leaves scale	Expected. This is a filtration system, not a softener — it does not remove hardness minerals. A scale inhibitor cartridge protects plumbing but won’t soften the water.

Scope note: This is a sediment-and-carbon filtration system for improving everyday water — it is not a certified microbiological purifier and does not soften water or remove dissolved minerals. Do not use it to make microbiologically unsafe water safe to drink; on an untested well or under a boil-water advisory, treat your water accordingly first.

Please note: Filter life and reduction performance depend on your water chemistry, pressure, and usage, so results vary from home to home. This product is not certified to treat water of unknown quality and is not a substitute for testing your water. Descriptions use general, qualified language and are not health claims. When in doubt, test your water or ask us and we’ll help you build the right stack.