RO membranes need cleaning when scale, biofilm or silt builds up on them. Regular cleaning, done before the membranes are badly fouled, restores output and extends membrane life.
Quick answer: clean when normalised output drops by about 10 to 15% or pressure drop rises by about 15%. Use a high pH cleaner for organics and biofilm and a low pH cleaner for scale and metal oxides, circulating each through the membranes at low pressure.
When to clean
Compare today's readings with readings taken when the membranes were new or freshly cleaned, at the same temperature and feed conditions. Clean when:
- Normalised permeate flow has dropped by about 10 to 15%.
- Pressure drop across a stage has risen by about 15%.
- Salt passage (permeate TDS) has risen noticeably.
Waiting longer makes fouling harder to remove, and some of the lost output may never come back.
Which cleaner to use
| What is fouling the membrane | Typical sign | Cleaner |
|---|---|---|
| Calcium carbonate, sulphate scale, iron and metal oxides | Output falls, last stage worst | Low pH cleaner: Zyax ZYPERM 210 |
| Biofilm, slime, oil and organics, silt | Pressure drop rises, first stage worst | High pH cleaner: Zyax ZYPERM 220 |
| Bacterial growth | Slime in cartridge housings, rising pressure | Clean, then a membrane-safe biocide: Zyax ZYPERM 310 |
Details for each grade are on the RO membrane cleaner and RO biocide pages.
How to clean RO membranes, step by step
- Flush the system with RO permeate or clean, chlorine-free water.
- Prepare the solution in the cleaning tank with permeate water, and check its pH and temperature against your membrane manufacturer's limits.
- Circulate the solution through one stage at a time at low pressure, so it cleans without pushing much water through the membranes.
- Soak the membranes in the solution, then circulate again.
- Flush thoroughly with permeate until the pH of the rinse water is back to normal.
- Repeat with the second cleaner if fouling is mixed, usually high pH first, then low pH.
- Restart and send the first permeate to drain until quality is back to normal. Record the new readings as your clean baseline.
Keep membranes cleaner for longer
- Dose the right antiscalant continuously.
- Remove chlorine before the membranes with sodium metabisulphite or carbon.
- Change cartridge filters on time.
- Store membranes in a preservative solution during long shutdowns.
Want help choosing a cleaner? Share your plant readings and water report on WhatsApp.
Ask on WhatsAppFrequently asked questions
When should RO membranes be cleaned?
Clean when normalised permeate flow drops by about 10 to 15%, when pressure drop across the membranes rises by about 15%, or when salt passage increases noticeably, compared with readings from when the membranes were clean.
Should I clean with low pH or high pH first?
Use high pH first for organic fouling, biofilm and silt, and low pH first for scale and metal oxides. Many plants run both, high pH first, when fouling is mixed.
Can I use acid or caustic straight from the drum?
Use a cleaner made for membranes and stay within the pH and temperature limits set by your membrane manufacturer. Harsh chemicals can damage polyamide membranes permanently.
How long does an RO cleaning take?
A full clean, with circulation, soaking and flushing for each cleaner, usually takes several hours per stage.
