my apec ro water tastes weird or salty after a few months. is the membrane bad?

Diagnosis

A salty, metallic, or "off" taste in an APEC ROES-50 system after a few months usually indicates "membrane breakthrough" or "TDS creep." In a healthy system, the semi-permeable membrane rejects up to 98% of dissolved salts and minerals. However, if the membrane has developed microscopic tears or has become fouled by chlorine (which eats through the polyamide layer), dissolved solids leak through into the product water. This is often caused by the first two pre-filters (sediment and carbon) becoming saturated, allowing chlorine to reach and degrade the membrane. Another common cause is a failure in the Automatic Shut-Off Valve (ASO) or a leaking check valve. If the system doesn't shut off completely, "cross-contamination" occurs where concentrated brine water from the waste line seeps back into the reserve tank or the product line. You can confirm this by using a TDS (Total Dissolved Solids) meter. Measure the tap water, then measure the RO water. If the RO water is more than 10-15% of the tap water's TDS value, the membrane is failing. If the taste only occurs after the system has sat idle overnight, the issue is likely a faulty check valve causing brine migration.

How to Fix It

To resolve the taste issue and restore water purity, follow these steps to replace the filtration stack and the membrane:

1. Shut off the cold water supply valve and close the ball valve on top of the storage tank.
2. Open the RO faucet to release all internal pressure.
3. Use the provided housing wrench to unscrew the three pre-filter canisters. Discard the sediment filter and the two GAC (Granular Activated Carbon) filters. Clean the inside of the housings with mild soap and water.
4. Unscrew the membrane housing cap (the horizontal tube). Carefully pull out the old RO membrane. If it feels slimy or looks discolored, it was fouled.
5. Insert a new APEC-compatible 50 GPD (Gallons Per Day) membrane. Push it firmly until it seats fully into the housing; you should feel it "click" or lock into place to ensure a tight seal.
6. Install new pre-filters. Ensure the sediment filter is in the first stage, followed by the carbon filters. Tighten the housings hand-tight, then give them a quarter-turn with the wrench.
7. Replace the final polishing filter (the small inline carbon filter) if it has been in use for more than 6-12 months, as this removes the "stale" taste from the storage tank.
8. Slowly open the water supply and check for leaks. Flush the system by filling and draining the storage tank twice before drinking.

If That Didn't Work

• Replace the Check Valve: If the taste returns after the system sits idle, the one-way check valve (usually a small elbow fitting where the membrane housing meets the tubing) is leaking. This allows salty brine to flow backward into your pure water line. Replace the check valve with a new elbow fitting to ensure a one-way flow.
• Inspect the ASO Valve: If you hear the system constantly running (water flowing to the drain) even when the tank is full, the Automatic Shut-Off Valve is faulty. This prevents the membrane from resting and can lead to premature degradation and taste issues. Replace the ASO valve.
• Sanitize the System: If the taste is "musty" rather than salty, bacteria may have colonized the storage tank. Drain the tank and use a food-grade sanitizing solution or a small amount of unscented bleach in the pre-filter housings to flush the system.
• Check for Air Leaks: Inspect the tubing connections for tiny pinhole leaks. If air is being sucked into the system, it can alter the pressure dynamics and cause the membrane to operate inefficiently, allowing more TDS to pass through.

Heads Up

• Pre-Filter Priority: Never skip the carbon pre-filter changes. The membrane is extremely sensitive to chlorine; if the carbon filters fail, the membrane will be destroyed in a matter of weeks.
• TDS Monitoring: Buy a digital TDS meter. Testing your water every 3 months is the only way to know if the membrane is failing before you actually taste the salt.
• Tank Pressure: Check the air pressure in the storage tank with a tire gauge. It should be 7-10 PSI when empty. If it is too high, the system may not fill properly, leading to "stagnant" water tastes.
• Avoid Kinking: Ensure the 1/4" poly tubing is not kinked or pinched behind the cabinetry, as this restricts flow and can cause pressure spikes that damage the membrane.