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Clear water starts with the kit you rarely see
When you look at a sparkling pool, you’re seeing the result of lots of quiet work going on behind the scenes. Most of it happens in the plant room, where the pump and filter run day after day without much fuss.
Good pool filtration is the backbone of clean, healthy water. Chemicals do an important job, but they can’t do it alone. Without a filter to trap dirt, debris and tiny particles, even perfectly balanced water soon turns dull and cloudy.
In this guide we’ll explain how your filter system works, the main types of filter, how pumps and run times fit in, and the simple habits that keep everything running smoothly. No jargon, we promise.
The short version
Water is drawn out of the pool, pushed through a filter that catches dirt, warmed and treated if needed, and then returned to the pool clean. That loop runs again and again. The better it works, the clearer your water.
The water in your pool is always on the move
It’s easy to think of pool water as still. In fact, it’s constantly circulating through a loop of pipes and equipment.
How water leaves the pool
Water is drawn out through skimmers at the surface and a main drain or suction point lower down. The skimmers are especially useful. They catch floating leaves, insects and oils before they sink and spread.
The pump does the heavy lifting
The pump pulls water from the pool and pushes it through the rest of the system. Before the water reaches the pump, it passes through a strainer basket that catches larger debris like leaves and hair. This protects the pump from damage.
Through the filter and back again
Next, the water passes through the filter, where smaller particles are trapped. It may then go through a heater and a treatment system before returning to the pool through inlets. These inlets are positioned to keep the water moving, so there are fewer still corners where dirt can settle.
Why circulation matters
Moving water is harder for algae and bacteria to settle in. Good circulation also spreads chemicals and heat evenly, so every part of the pool gets the same treatment.
That’s why filtering and circulation are really two halves of the same job. A brilliant filter can’t help if water never reaches it from the far corners of the pool. And perfect circulation won’t help much if the filter is clogged. The two need to be planned together, which is something we think about carefully when designing a new pool.
There are three main types of pool filtration
Most home pools use one of three filter types. Each works in a slightly different way, and each has its own strengths.
Sand and glass media filters
These are the most common type in UK home pools. A large tank is filled with a filter media, traditionally a specially graded sand. As water is pushed through, particles get caught between the grains.
Many owners now choose recycled glass media instead of sand. It works in a similar way, and many people find it filters well and needs cleaning less often, though results vary from pool to pool.
Media filters are cleaned by backwashing, which we’ll explain shortly. The media itself lasts several years before it needs replacing.
Cartridge filters
A cartridge filter uses pleated fabric cartridges to trap dirt. They can catch finer particles than a typical sand filter and don’t need backwashing. Instead, you take the cartridge out and rinse it with a hose.
Cartridges need replacing from time to time, and it’s handy to keep a spare so the pool can keep running while one is being cleaned.
Diatomaceous earth filters
These filters, often called DE filters, use a fine powder made from fossilised algae. The powder coats a set of grids inside the filter and traps extremely small particles. They can give very polished water.
They do need more careful handling. The powder is very fine, so it’s sensible to wear a dust mask and follow the product guidance. Disposal rules can vary too, so check what applies in your area.
Which is best?
There’s no single winner. It depends on your pool, how it’s used and how hands-on you want to be. We’ll recommend the right setup as part of your pool project.
Pumps and run times make or break pool filtration
A filter can only clean the water that reaches it. That’s why the pump, and how long it runs, matters so much.
Choosing the right pump
The pump needs to be correctly sized for your pool and your filter. Too small, and the water isn’t turned over often enough. Too large, and you can waste energy and even push water through the filter too fast to clean it properly.
Many modern pools use variable speed pumps. These can run gently for long periods and speed up when needed, such as for backwashing or running a water feature. They’re generally quieter, and running at lower speeds tends to be kinder on energy use.
How long should the pump run?
This is one of the questions we’re asked most. The answer depends on your pool’s size, how busy it is, the weather and the equipment you have.
As a rough idea, the aim is to pass all the water in the pool through the filter a few times a day during the swimming season. In practice, many pools run for several hours a day in summer and less in cooler months. Your installer or service engineer can set a timer that suits your pool.
Signs you may need longer run times
You might need to run the pump for longer if:
- The water looks dull or slightly hazy.
- The pool has been busy, for example after a party.
- There’s been a heatwave, or lots of leaves and pollen.
- You’ve had to add treatment chemicals to correct a problem.
If the water turns milky, our guide to clearing cloudy pool water can help you work out why.
Backwashing keeps a media filter working well
Over time, the media fills up with the dirt it has trapped. The water struggles to get through, and filtering becomes less effective. Backwashing reverses the flow to flush that dirt away.
Why backwashing matters
A clogged filter is one of the most common reasons for dull water we see on service visits. Regular backwashing keeps your pool filtration working at its best and puts less strain on the pump.
Knowing when to backwash
Most filters have a pressure gauge. Make a note of the reading when the filter is clean. When the pressure rises noticeably above that level, it’s usually time to backwash. Your installer can tell you the right range for your system.
A simple backwashing routine
Every system is slightly different, so always follow the instructions for your equipment. A typical routine looks like this:
- Switch the pump off.
- Set the multiport valve to the backwash position.
- Make sure the waste line is open and directed to a suitable drain.
- Switch the pump on and let it run until the water in the sight glass runs clear.
- Switch the pump off and set the valve to rinse.
- Run briefly on rinse to settle the media, then switch off.
- Return the valve to filter and switch the pump back on.
Never move the valve while the pump is running, as this can damage the valve and seals.
Topping up afterwards
Backwashing removes some water, so check the level and top up if needed. It’s also a good moment to test and rebalance the water.
Everyday habits help your filter do its job
A little regular care makes a big difference to how well your filter works and how long it lasts.
Weekly checks
- Empty the skimmer baskets. Full baskets reduce flow.
- Check the pump strainer. Clear out leaves, hair and debris.
- Look at the pressure gauge. Backwash or clean the filter when needed.
- Brush and vacuum. Loosened dirt is then picked up by the filter.
A robotic cleaner can take care of much of the floor and wall cleaning for you, which reduces the load on the filter.
Keeping the water balanced
Filtration and chemistry work together. Balanced water helps the filter work well and protects the equipment from scale and corrosion. Our plain English guide to pool chemicals explains the basics.
If you handle chemicals yourself, always follow the label, wear gloves and eye protection, never mix chemicals, add chemical to water and never water to chemical, keep swimmers out until the water is balanced, and store everything away from children and pets.
Using a cover
A cover keeps leaves and dust out of the pool when it’s not in use, which means less work for your filter. It also helps hold heat in.
Looking after the system through winter
If your pool is used less over the colder months, the filter and pump still have a job to do. Many owners keep the system running for shorter periods to stop the water going stagnant and to protect pipework from frost. Others close the pool down properly for the season. Your service engineer can advise on the best approach for your pool and your equipment.
Upgrading an older system
If your pool is a few years old, the equipment may not be as efficient as it could be. An older pump might be noisy, or the filter might be too small for how the pool is used now. Upgrading the pool filtration kit can make a real difference to water quality and to how easy the pool is to live with. We’ll give you a realistic estimate after looking at your setup.
Regular servicing
Seals, valves and pumps wear over time. A regular service spots small problems before they become bigger ones. Our guide to swimming pool maintenance covers a full routine, and we offer servicing and repairs if you’d rather leave it to us.
On a typical service visit, an engineer will check the pump and seals, look at the filter and its pressure readings, inspect valves and pipework for leaks, and test the water. It’s a good chance to ask questions too. Many owners find a spring and autumn check gives real peace of mind.
Pool filtration questions we get asked a lot
Can I turn the pump off overnight?
Many owners run their pump on a timer rather than all day and night. The right schedule depends on your pool, so ask your installer or service engineer.
How often should I replace the filter media?
It depends on the type of media and how the pool is used. Sand and glass media typically last several years, but your service engineer can check its condition.
Why is my pressure gauge reading high?
Usually it means the filter is dirty and needs a backwash or clean. If the pressure stays high afterwards, there may be a blockage, so ask for a check.
Why is my water still cloudy when the pump is running?
The filter may need cleaning, the run time may be too short, or the water chemistry may be off. Test the water first, then look at the filter.
Does a small pool need the same filter as a big one?
No. Filters and pumps should be sized to suit the volume of water and how the pool is used.
Good pool filtration means more time enjoying the water
When your filter and pump are well chosen and well looked after, you’ll spend less time worrying about the water and more time swimming in it. A few simple habits go a long way.
If you’d like help with your current setup, or you’re planning a new pool and want the equipment done right from the start, we’d be glad to help. You can also explore our full range of pools to see what we install.
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.
