How to clean a pool filter: ensure your water stays fresh and clean

Learning how to clean a pool filter is key to enjoying water that is clean and hygienic. Like every other type of filter, it will need regular cleaning, especially when it's in use. And if you are about to cover your pool for the winter, you'll need to give the filter (and your pool) one final thorough clean. 

Filter cleaning is an essential element of looking after your backyard pool. We've asked plumbing and home maintenance experts to give their best tips for doing this job right. They also answered a couple of common questions about the frequency of this necessary task and when to replace your filter. 

Why it's important to know how to clean a pool filter

If you are tempted to skip cleaning your pool filter, resist the temptation. We've asked Alex Woollam, a licensed plumber and the founder and CEO of Waterline Plumbing, why cleaning a pool filter is so important. 

'Pool filters are essential in removing dirt, dust, and other water contaminants,' says Alex. 'This helps ensure that you get clean and safe swimming pool water every time you go for a swim. Not only do pool filters remove impurities, but they also help to reduce chlorine levels and optimize the pH of the water.'

Skip cleaning your filter and 'your swimming area will become overcrowded with bacteria and unwanted algae, eventually leading to skin or eye irritation.' 

To prevent issues such as black algae or mustard algae, make sure you perform this essential pool maintenance task regularly. And bear in mind, that cloudy pool water can also be a sign of a dirty filter. 

How to clean a pool filter in 5 easy steps

Follow these basic steps to keep your pool filter clean throughout the year. It's also a good idea to make this part of your process for winterizing a pool. 

1. Turn off the system

Karen Barrigan, a home maintenance expert at Housetastic.co.uk, cautions swimming pool owners against working with any pool equipment while the system is on. 'Always make sure the first thing you do is turn the pump off.' The same rules apply when cleaning a hot tub filter safely too. 

Then, bleed the filter tank of air by opening the air relief valve. 'Never attempt to open the pool filter tank while there is still pressure within the system. This could damage the filter or may result in you injuring yourself.' 

2. Open the filter tank and remove the cartridges

Remove the clamp on the lid and open up the lid. The clamps can vary from model to model so be sure to check your user manual for the correct way to remove this.

Once the lid is off the filter tank, remove the cartridges so they’re ready for cleaning. Karen Barrigan reminds pool owners to always refer to the user manual 'for the correct way to remove the filter cartridges in your particular model.'

Your pool filter cartridges can last for around three years before they need to be replaced, depending on the size and make of your filter. Each time you clean them, you should inspect them for damage. Karen Barrigan's top tip is to do 'a quick visual check for tears in the pleats, cracks in the plastic, or any other visual signs of damage. If you notice any damage, you should replace the cartridge.'

3. Remove debris from your filter

Spray the cartridges with your garden hose. This should help to remove most of the debris from between the pleats.

Start at the top of the cartridge and work your way down. After you’ve rinsed the whole cartridge, turn it upside down and do the same again.

If your hose fails to remove all of the debris, try a pressure washer. 'If this still fails to remove all of the debris, consider purchasing a gentle brush or a device that is designed for removing dirt from pool filters', Karen recommends. Brush sparingly and very lightly as brushing can wear down the cartridge.

A pool cartridge cleaning brush can be bought on Amazon. 

4. Degrease the cartridge

A pool degreaser or cartridge cleaner (both available from Amazon) are best for removing waste and grease from the cartridge. These are available online, in DIY stores, and in pool supply stores.

Spray the product on the cartridge and be sure to cover all of the surface areas. Leave it on the cartridge for the recommended amount of time. 

Then, rinse it off with your hose. If the grease is quite stubborn, you may need to leave the cartridges to soak overnight.

5. Reassemble your cartridges and filter

Once the cartridges are clean, you will then need to replace them in the filter tank. Reassemble all of the necessary attachments. Ensure everything is tightly closed. Then, close the air release valve.

Turn on the pump to ensure everything is working properly. While the pump is running, open the air relief valve to release any excess air from the system. When water starts consistently spraying out of the valve, this means all of the air will be removed from the system.

Check the pressure to ensure it is falling within the appropriate range for your filter.

How often should you clean a pool filter? 

Professionals recommend cleaning the pool filter regularly, particularly during the swim season. As a rough guide, you should be looking to clean it once a month when the pool is being used frequently in the summer. This frequency can be reduced when the pool is being used less at other times of the year. Keeping on top of this task is essential to prevent and get rid of algae in a pool. 

However, Hugo Guerrero, a certified House Cleaning Technician (HCT) at Mattressive, recommends thinking beyond just the filter, too, as it may not always be the reason your pool isn't as clean as it can be. 'You should also check for clogged or damaged parts of your filter system that may be causing your filter to become clogged with debris.

'This includes debris such as leaves and twigs that may have gotten into your filter system or any other parts of your pool system that could have been damaged by falling trees during harsh weather conditions.' So, if your filter is new but your pool water is not as clean as it should be, you need to perform a thorough inspection of your entire system. 

How do I know if my pool filter needs replacing?

It can be tricky to know when your pool filter needs more than just a clean, but the method used most often for determining if a pool filter needs replacing is the bath soak method. 

'The water bath soak method is a simple and safe way to test if your pool filter needs replacement,' says Alex Woollam. All you need is some fresh (or pre-treated) water, and a pot or container big enough to fit the pool filter.

'Put the freshly treated water in the pot or container, place the pool filter over it, and carefully immerse it so that its surface is submerged. If there's an increase in chlorine levels after 72 hours of soaking, then your pool filter may need to be replaced. This is a quick and easy way to determine if you need to get new filters for your swimming pool.'

If you cannot conduct a bath soak test or would like help determining whether or not your filter needs replacing, contact a professional swimming pool contractor for assistance.