How to Clean a Pool Filter (and When to Backwash)

A clean filter is the quiet hero of clear pool water

Your filter does a lot of work you never see. Every hour the pump runs, it pushes water through the filter, which traps dust, pollen, hair, skin cells and tiny bits of debris. Over time, all of that builds up. The filter slowly clogs, the water flows less freely and the pool starts to look a little less sparkling.

The good news is that looking after it is simple once you know the routine. In this guide we explain how to clean a pool filter in plain English, from spotting the signs that it needs attention to the steps for the most common types.

We’ll also cover how often to do it, what to avoid and when it makes sense to call in an engineer. If you’d like a broader picture of how the whole system works, our guide to pool filtration is a good place to start.

Safety comes first, every time

Before you open, move or adjust anything on your filter, switch the pump off at the controls and make sure the power is isolated. Never touch electrical parts, wiring or control panels. Always follow the manufacturer’s instructions and the handover guidance you were given with your pool. If anything looks unfamiliar or you’re not sure, stop and call an engineer.

Knowing how to clean a pool filter starts with knowing which one you have

Most home pools in the UK use one of two main types of filter. They do the same job, but they’re cleaned in quite different ways.

Sand and media filters

These are large tanks, usually standing in the plant room or equipment area. Inside is a bed of filter media. That might be graded sand or a glass or synthetic alternative. Water passes down through the bed and the dirt gets caught in it.

You’ll normally see a multiport valve on the top or side of the tank. It has a handle with several settings, such as filter, backwash, rinse, waste, recirculate and closed. You’ll also usually find a pressure gauge nearby.

Media filters are cleaned by reversing the flow of water through the bed, which lifts the trapped dirt and sends it out to waste. This process is called backwashing.

Cartridge filters

A cartridge filter has one or more pleated fabric cartridges inside a housing. The pleats give a large surface area that catches fine particles. There’s no multiport valve to worry about. Instead, you take the cartridge out and rinse it.

Cartridge filters are common on spas and some smaller pools. Some larger pools use them too.

Not sure which you have?

Your handover pack should tell you. If it doesn’t, take a photo of your equipment and ask whoever services your pool. If we installed it, just get in touch and we’ll talk you through it. You may also find our guide to the pool plant room helpful for getting to know the equipment.

Your filter will tell you when it needs cleaning

Knowing how to clean a pool filter is only half the job. Knowing when to do it matters just as much. Cleaning on a fixed date isn’t the best approach. It’s better to watch for the signs that it’s getting clogged. There are three main clues.

The pressure gauge is creeping up

This is the most reliable sign. When the filter is clean, the gauge shows a certain reading with the pump running. Make a note of that figure. It’s your clean starting point.

As dirt builds up, water struggles to pass through, so the reading rises. Your installer or the manufacturer’s instructions will tell you how much of a rise means it’s time to clean. As a rough rule of thumb, a clear rise above your clean starting point is your cue.

The return flow feels weaker

Put your hand near the return jets, where water flows back into the pool. If the flow feels noticeably weaker than usual, the filter may be clogged. It could also be a full skimmer basket or pump strainer basket, so check those first.

The water isn’t as clear as usual

A slightly hazy pool can point to a filter that isn’t doing its job. Cloudy water has several possible causes, including water chemistry, so test the water too. If the balance looks fine and the filter pressure is high, the filter is the likely culprit.

How to clean a pool filter when it’s a sand or media filter

Backwashing a media filter only takes a few minutes. The steps below are general. The exact order and settings can vary between systems, so always check the manufacturer’s instructions and your handover guidance.

Get ready

• Switch the pump off at the controls before you touch the valve. Moving the handle while the pump is running can damage the valve and its seals.
• Check that the waste line or hose is in place and that the water has somewhere suitable to go.
• Make sure the pool water level is high enough, as backwashing removes some water.

Work through the steps

1. Turn the pump off. Wait for it to stop completely.
2. Set the valve to backwash. Press down on the handle and turn it to the right setting. Make sure it clicks firmly into place.
3. Turn the pump back on. Let it run until the water in the sight glass or waste line looks clear rather than cloudy. This usually takes a couple of minutes.
4. Turn the pump off again.
5. Set the valve to rinse. This settles the media bed back into place and flushes any loose dirt out to waste.
6. Run the pump on rinse briefly, again until the water runs clear, then switch the pump off.
7. Return the valve to filter. Check it’s seated properly.
8. Switch the pump back on and note the new pressure reading. It should be close to your clean starting point.

Top up afterwards

Because backwashing and rinsing send water to waste, check the level afterwards and top up if needed. Fresh water can nudge your balance, so test the water and adjust gently if necessary.

How to clean a pool filter cartridge without damaging it

Cartridges need a gentler approach. The fabric pleats are easy to tear if you’re rough with them.

Rinsing a cartridge

1. Switch the pump off and isolate the power.
2. Release any pressure using the air bleed valve, if your filter has one.
3. Open the housing following the manufacturer’s instructions.
4. Lift out the cartridge carefully.
5. Rinse it with a garden hose. Work from the top down, spraying between the pleats at an angle. A gentle to medium spray is best. Avoid a pressure washer, which can damage the fabric.
6. Check the cartridge for tears, flattened pleats or a crumbling end cap.
7. Clean the housing seal or O-ring, and check it for damage. Refit the cartridge and close the housing securely.
8. Switch the pump back on, bleed any air and check the pressure reading.

Keeping a spare

Some owners keep a second cartridge. That way you can swap in a clean one straight away and let the other dry out properly before its next clean.

An occasional deep clean keeps your filter working well

Most guides on how to clean a pool filter stop at the regular routine. A rinse or backwash removes most of the loose dirt. Over time, though, oils, lotions and minerals can build up in a way that a simple rinse won’t shift.

For a cartridge, that might mean soaking it in a filter cleaning solution now and then. For a media filter, a specialist media cleaner can help break down oily deposits. If you use any cleaning product, follow the label exactly. Wear gloves and eye protection, never mix chemicals and store products safely away from children and pets.

Filter media and cartridges don’t last forever. A cartridge that won’t come clean, or a media bed that has clumped or channelled, will need replacing. Your service engineer can check this for you and advise on timing.

Don’t clean too often

This one surprises many people. A slightly dirty filter actually traps fine particles better than a spotless one, because the trapped dirt helps catch smaller bits. Cleaning too often wastes water and can make the filter less effective. Go by the pressure gauge rather than the calendar.

Fit it into your routine

Checking the pressure gauge is a quick weekly job. Our pool maintenance checklist shows how filter care fits in alongside testing, skimming and emptying baskets.

Where your waste water goes matters more than you might think

When you backwash or rinse, the water leaving the filter is dirty and contains pool chemicals. It needs to go somewhere suitable.

Rules on where this water can go vary between areas. In some places it should go to a foul drain rather than a surface water drain. Don’t let it run into ponds, streams or neighbouring gardens. Check with your local council or water company if you’re unsure what’s allowed where you live. Your installer should also have set up a suitable outlet when the pool went in.

Saving water where you can

Only clean when the gauge tells you to, and stop as soon as the water runs clear. Both habits cut down how much water you send to waste.

When to leave it to an engineer

Once you’ve learned how to clean a pool filter, most of the job is well within reach for a confident owner. There are times, though, when it’s better to call in help:

• The pressure stays high even after cleaning.
• The pressure drops very low, or the gauge reads zero with the pump running.
• You see sand or media coming back into the pool.
• The valve is stiff, leaking or won’t click into place.
• There’s water leaking from the tank, housing or pipework.
• The pump sounds different, hums without starting or trips the power.
• Anything involves electrics, wiring or control panels.

Never try to repair electrical equipment yourself. If in doubt, switch off and ask a qualified engineer.

We offer aftercare, servicing and repairs for the pools, swim spas and spas we install. A regular service includes a proper check of your filter and pump, so small issues are caught early.

Pool filter questions we get asked a lot

How often should I clean my pool filter?

There’s no fixed date. Watch the pressure gauge and clean when it rises by the amount your installer or manufacturer suggests. In a busy summer that may be more often than in a quiet spring.

Can I clean the filter with the pump running?

No. Always switch the pump off before moving the valve or opening the filter housing. Moving the valve while the pump runs can damage it.

Why is my water still cloudy after cleaning the filter?

The filter may need a deep clean, or the cause could be water chemistry. Test the water and check the pump is running for long enough each day. If it persists, ask an engineer.

How long do cartridges last?

It depends on use and how well they’re looked after. Replace a cartridge when it’s torn, misshapen or won’t come clean after a proper rinse.

Do I need to top up the pool after cleaning the filter?

Often, yes. Backwashing and rinsing send some water to waste. Check the level and top up so the skimmers keep working properly.

Can HiLife look after my filter for me?

Yes. We offer aftercare, servicing and repairs for the pools, swim spas and spas we install. Get in touch and we’ll talk you through the options.

Learning how to clean a pool filter keeps your pool clear for longer

A clean filter means clearer water, a happier pump and fewer surprises. Once you know the routine, it becomes a quick and satisfying part of your routine. Keep an eye on the pressure gauge, switch off before you touch anything and follow your manufacturer’s instructions and handover guidance. Don’t hesitate to call an engineer if something doesn’t seem right.

If you’re still at the planning stage and want a pool that’s easy to look after from day one, explore our full range of pools and see what might suit your garden.

Call us on 01483 323 676 or email hello@hilifepools.co.uk for a friendly, no-pressure chat, or get in touch online and we’ll come back to you.