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4-in-1 Remineralization Inline Filter — 10″ × 2″
MINERAL4IN1
Amazon: 4in1Mineral38 (3/8″)
This page covers where the filter goes, how to install it, when to change it, how to test pH and TDS, and the parts that fit it.
Is this your filter?
Check these against the filter in your hand. All four should match.
- ✓A white inline filter about 10″ long and 2″ across
- ✓The label says 4-in-1 mineral or remineralization filter
- ✓1/4″ threaded ports at both ends and a FLOW arrow on the label
- ✓It came with elbow adapters for 3/8″ (or 1/4″) tubing
Mineral, alkaline or carbon? Check the label
- 4-in-1 mineral / remineralization — this page.
- 3-in-1 alkaline — a different filter with a different change schedule. See the alkaline filter →
- Carbon, sediment, DI or specialty — see the full guide for all inline filters. Inline filter guide →
Specifications
| Model / SKU | MINERAL4IN1 · Amazon: 4in1Mineral38 |
| Media | Four-media blend: tourmaline, maifan stone, bioceramic and alkaline/mineral media |
| What it does | Adds calcium, magnesium and other minerals to RO water and raises its pH |
| Size | 10″ × 2″ |
| Connection | 1/4″ FPT ports · elbow adapters for 1/4″ or 3/8″ OD tubing |
| Flow | 0.5 GPM |
| Pressure / temperature | Max 90 PSI · 36–100°F, cold water only |
| Typical life | 6–12 months, or about 400 gallons |
| Brand | MyWaterClub |
Reorder this filter
This filter · MINERAL4IN1
4-in-1 Remineralization Inline Filter
On MyWaterClub.com you choose adapters for 1/4″ tubing, 3/8″ tubing or both, and the price per filter drops when you buy more. The Amazon listing is the 3/8″ version.
Where it goes
A remineralizing filter is always the last stage, and it is for RO water only. It adds minerals back after the RO membrane has removed them.
| Your setup | Order of stages |
|---|---|
| Under-sink RO | Pre-filters → RO membrane → storage tank → carbon post filter → 4-in-1 mineral → faucet |
| Countertop RO | Faucet adapter → sediment → carbon → RO membrane → carbon post filter → 4-in-1 mineral |
| Fridge or ice maker line | Only when the line is fed by RO water: RO system → 4-in-1 mineral → appliance |
Where not to use it
- On a plain tap water line — tap water already has minerals.
- On an air humidifier — added minerals leave white dust.
- Before the RO membrane — the membrane would remove what the filter adds.
- Before any carbon filter, including the carbon post filter — carbon takes out part of the minerals this filter adds. Put the 4-in-1 after it.
Connections
Before you cut anything
- Check your tubing size. It is either 1/4″ OD or 3/8″ OD, usually printed on the tubing. Use the matching adapters. Never force 1/4″ tubing into a 3/8″ port, or the reverse.
- Water must flow the way the arrow on the label points.
- You need a tubing cutter (or a sharp utility knife), PTFE thread tape, a towel and a small bucket.
- Fit the adapters to the filter. Wrap the adapter threads with 3–4 turns of PTFE tape, clockwise. Hand-tighten, then add a quarter to half turn with a wrench. Do not overtighten — the filter body is plastic and can crack.
- Cut the tubing square. A 90° cut. A cut off by about 15° or more will leak. The last inch should be round, smooth and free of scratches.
- Remove any blue C-clips from the adapters. A clip left in stops the tube from seating.
- Push the tube in until it stops, then pull gently to confirm it holds.
- Refit the blue C-clips on every quick-connect port.
To remove a tube later: turn off the water and release pressure, take off the C-clip, push the collar in toward the filter and pull the tube out while holding the collar.
Installing on an under-sink RO
First time? Watching a short video helps: search YouTube for “add inline filter to RO system”.
- Shut off the RO water supply and the tank valve, then open the RO faucet to release pressure.
- Find the spot: after the storage tank and the carbon post filter, right before the faucet.
- Check the tubing size and that the adapters match, then cut the tubing square over a towel.
- Connect the filter with the FLOW arrow pointing toward the faucet, and refit the C-clips.
- Secure the filter with a clip: a 2.5″ × 2″ clip onto the membrane housing, or a 2″ × 2″ clip onto another inline filter.
- Open the supply and tank valves. Check for leaks now, after 10 minutes, and the next day.
- Flush the new filter for at least 5 minutes with the RO faucet open. Let the tank fill, then discard the first full tank.
- Write the install date on the label.
Countertop RO: follow your system’s manual. Keep this filter last, after the carbon post filter, and flush it for at least 5 minutes before drinking the water.
When to change your filter
| Filter | Typical interval | Change sooner if… |
|---|---|---|
| 4-in-1 mineral filter | 6–12 months or about 400 gallons |
The taste changes, or the pH falls back toward plain RO water |
Intervals are typical estimates. Your source water, flow and usage set the real schedule.
Testing pH and TDS
- Wait one week after installing a new filter. The first water through a mineral filter reads much higher than normal.
- TDS goes up after this filter. That is expected — it adds minerals. Measure TDS right after the RO membrane to judge the membrane.
- pH: plain RO water is usually slightly acidic, about 6–7. This filter raises it. Run the water for a minute and test right away, because RO water’s pH drops within minutes in an open cup.
- Meters drift in RO water. Calibrate a pH meter with pH 7 and pH 4 or 10 buffers, or use pH test drops made for low-mineral water.
Full testing steps in the inline filter guide → · Digital pH meter →
Parts that fit this filter
| Part | Notes |
|---|---|
| 1/4″ thread × 3/8″ quick-connect elbow, 2-pack | Adapters for 3/8″ tubing |
| 1/4″ quick-connect elbow, threaded, 2-pack | Adapters for 1/4″ tubing |
| Blue C-clips for 3/8″, 10-pack | Locks the tube in a 3/8″ port · 1/4″ clips |
| 2.5″ × 2″ mounting clips, 2-pack | Clips the filter onto an RO membrane housing · 2″ × 2″ clips · 2″ screw-mount clips |
| Tubing cutter with release tool | Square cuts on 1/4″ and 3/8″ tubing |
| 3/8″ OD tubing, white | If you need extra length · 1/4″ tubing |
All tubing, clips and fittings →
Common questions
| What you’re seeing | Most likely cause |
|---|---|
| Cloudy or milky water from a new filter | Fine mineral particles or trapped air. Flush for at least 5 minutes; bubbles clear within a day or two. |
| Drip at a quick-connect port | Tube not fully in, scratched or cut at an angle, or the C-clip was left in. Release, recut square, push it fully in and refit the clip. |
| Drip at a threaded port | Too little thread tape, or cross-threaded. Remove, re-tape and start it by hand before tightening. |
| Low flow at the faucet | Filter installed backward, kinked tubing, or a filter past its date. Check the arrow, the tubing and the install date. |
| TDS is higher after this filter | Expected — the filter adds minerals. Judge the RO membrane by testing before this filter. |
| pH readings jump around | Normal for pen meters in low-mineral water. Use pH test drops, or stir and wait for the reading to settle. |
| The taste went flat again | The media is used up. Time for a new filter. |
Need help?
Contact us
Send a photo of the filter label and your system, and we’ll tell you where it goes
Call or text (858) 345-7345. Bought on Amazon? You can also reach us through Amazon: Your Orders › Contact seller.
Scope note: This is a taste and mineral step for RO water, not a contaminant filter. It does not reduce chlorine, sediment or fluoride. Use it on municipally treated or otherwise microbiologically safe water. Descriptions refer to taste and mineral content only and are not health claims.
Please note: pH, mineral levels and filter life depend on your source water, flow rate, contact time and usage, so results vary from home to home. This product is not a substitute for testing your water.