Clean a pool filter when the pressure gauge says it is dirty, not on a fixed date. Sand filters are backwashed once the pressure has risen a set amount above the clean-filter reading; cartridge filters are lifted out and hosed down when the same rise appears. The exact trigger is in the manufacturer's manual, and how often you reach it depends on bather load, water clarity and what the filter is catching.
How Do You Know a Pool Filter Needs Cleaning?
Three signs, in order of reliability. First, the pressure gauge on the filter inlet: note the reading when the filter is freshly cleaned, write it on the vessel, and compare from then on. Second, flow: a return that is weaker than it used to be, or a flow meter creeping down, means water is struggling through. Third, the water itself. If clarity slips while chemistry is in range, suspect the filter before you suspect the chemicals.
Do not wait for the third sign. By then the filter has been under-performing for a while, and that costs more than the backwash does.
How Often Should You Backwash or Clean?
There is no honest universal number, and anyone who gives you one for every pool is guessing. A hotel pool with heavy evening use and a quiet outdoor pool in winter sit at opposite ends. What is universal is the method: log the clean-filter pressure, set a trigger, and record every cleaning. After a few months the log tells you your own interval.
Also clean after anything unusual: a heavy bather load, an algae episode, a flocculant dose or a fill with dirty make-up water.
What Is the Right Cleaning Method for Each Filter Type?
| Filter type | How it is cleaned | Watch out for |
|---|---|---|
| Sand | Backwash (reverse flow), then rinse to waste before returning to filter | Channelling and compacted bed: the pressure looks fine but water finds a path through. The sand eventually needs replacing |
| Cartridge | Remove, hose down pleat by pleat, soak if oily; replace when worn | Hosing at close range flattens the pleats and shortens cartridge life |
| Diatomaceous earth (DE) | Backwash, then recharge with fresh media | Handling and disposal of the media; follow local rules for the waste water |
| Public-pool multimedia vessels | Automatic or manual backwash, often with air scour, to a set programme | Backwash volume and rate set wrongly will either leave dirt behind or lose media |
How Do You Backwash a Sand Filter Step by Step?
- Switch the pump off before you move the multiport valve. Turning it under flow can damage the internals.
- Set the valve to backwash and start the pump.
- Watch the sight glass. Run until the water coming out is clear, not for a fixed time.
- Stop the pump, set the valve to rinse, and run briefly until the water is clear again.
- Stop the pump, return the valve to filter, restart, and note the new clean-filter pressure.
- Write the date, the before and after pressures and the backwash duration in the log.
On a public plant with automatic valves the sequence is programmed, but the principle holds: you are judging the result by the water and the pressure, not by the clock.
What Happens If You Clean the Filter Too Often, or Too Rarely?
Too rarely, and the bed or cartridge loads up. Flow falls, the pump works harder, fine particles pass through, and the water turns dull. Dirt held in the filter also keeps using up disinfectant, which pushes chemical demand up.
Too often, and you waste heated, treated water. A little dirt in a sand bed actually helps it catch finer particles, so a bed scrubbed spotless after every session performs worse for a short while. Backwash because it is needed, not as a ritual.
Does Better Water Treatment Mean You Can Skip Filter Care?
No, and this is where we are straight with you as a water-treatment supplier. NanoSWIM's nanobubble technology is installed inline in the existing circulation loop, after filtration. It does not replace the filter, and it does not do the filter's job. Fine particles and organic load still have to be removed mechanically, and a filter in poor condition will let the whole loop down. Correct filtration, sensible pH control and competent operation come first; treatment sits on top of them. Capital cost for treatment is also higher than for dosing pumps and drums, so there is no point buying it to cover for a neglected filter. You can read how the technology works for the mechanism.
What a clean filter does give a treatment loop is a stable, predictable flow. That matters for any system sized to a flow rate, including the NanoSWIM Pool System, which handles up to 500 m³/h.
What Should a Public Pool Document About Filter Care?
A Norwegian public pool operates under forskrift om badeanlegg, bassengbad og badstu, enforced by the municipal health authority, and an inspector may ask how the plant is run and maintained. A written log of pressures, backwashes and media inspections is the simplest thing you can show. See the standards page for the references buyers usually need, and our approach for public facilities for the wider picture.
Filter Care Checklist
- Clean-filter pressure written on or next to the vessel.
- Trigger pressure set from the manufacturer's manual.
- Every backwash or cartridge cleaning logged.
- Sight glass checked at each backwash.
- Sand or media inspected for channelling and wear on a routine schedule.
- Cartridges replaced when worn, not when they fall apart.
- Backwash water disposed of according to local rules.
In my own experience, you can tell how a plant is run from the backwash logbook before you have looked at a single valve. On one job I worked on myself, the book hung on a nail beside the filter and you could see the handwriting change from operator to operator, with the pressure readings quietly drifting. Nobody had done anything wrong, they just had no agreed trigger. Funnily enough, Norwegian buyers ask about logging and documentation much earlier in the conversation than anyone else, and this is why I understand it. A tidy book makes everything else easier to trust.
If you want to talk about your filtration and circulation alongside treatment, contact NanoSWIM in Bergen with your pool volume and flow rate, and we will tell you straight whether treatment adds anything or the filter is where to start.