How to Choose a Replacement Pool Filter Cartridge

Replacing a pool or spa filter cartridge sounds simple until you see how many look almost the same. A cartridge that's half an inch too long won't let the lid close, and one with the wrong center opening can let dirty water bypass the filter. This guide shows how to identify the cartridge you need, measure it correctly, and decide when it's time to replace it.

When should you replace a cartridge?

Regular cleaning extends cartridge life, but no cartridge lasts forever. Consider replacing yours when you notice:

• Filter pressure rises again soon after cleaning, or never returns to its normal clean reading
• Torn, flattened, or frayed pleats
• Cracked or separated end caps, or a crushed center core
• Fabric that feels hard or stiff even after cleaning, which often means mineral or oil buildup
• Cloudy water that doesn't clear even though chemistry and run time are correct

Our cartridge cleaning instructions cover routine cleaning. If a cleaned cartridge still can't hold a normal pressure, it's time for a new one.

Option 1: Start with the filter's model number

The easiest way to find the right cartridge is to look up your filter's model. The label is usually on the side of the filter tank or the lid. For spas, it may be stamped on the filter housing or listed in the owner's manual. With the model, you can find the original manufacturer's cartridge and any compatible replacements.

Option 2: Use the number on the old cartridge

Many cartridges have a part number printed on an end cap or the fabric. It may be the original manufacturer's number or a number from an aftermarket cartridge maker. Aftermarket brands publish cross-reference charts that match their cartridges to original equipment, so one number often leads you to several compatible options. Search the number in our store, or browse Filter Cartridges.

Option 3: Measure the old cartridge

If there's no readable number, measurements will get you there. Clean and dry the cartridge first if you can, then measure:

1. Length: from the outer face of the top end cap to the outer face of the bottom end cap. Don't include handles, threaded studs, or other parts that stick out. Note them separately.
2. Outside diameter: straight across the widest part, usually the end cap, through the center.
3. Top opening: the inside diameter of the hole in the top end cap, or note that it's closed, has a handle, or has a molded fitting.
4. Bottom opening: the same for the bottom end cap. Some spa cartridges have a threaded bottom; note the thread size if so.

Write down any special features as well: a handle, a threaded stud, a built-in core, or a slanted or notched end cap. Compare all of these with the product specifications before ordering. Length and both openings matter as much as diameter.

Understanding square footage

Cartridges are rated by filter area in square feet. More area generally means longer time between cleanings and lower operating pressure. For a replacement, match the original area, or choose a compatible cartridge with the same dimensions and a similar or higher rating. Don't move to a smaller cartridge to save money; less area means more frequent cleaning and higher pressure. For multi-cartridge filters, make sure you order the full set required by your filter.

Original vs. aftermarket cartridges

You'll often see both the equipment maker's original cartridge and compatible cartridges from filter brands such as Filbur. Compatible cartridges are designed to the same dimensions as the original. Differences between options can include the filter media, the number of pleats, the end cap material, and whether a reinforcing core is used. Whichever you choose, confirm that the dimensions and end cap style match your filter.

Installing a new cartridge

1. Turn the pump off and close any valves that isolate the filter. Open the air relief valve to release pressure. Never open a filter tank that's still under pressure.
2. Remove the clamp or lid following your filter's manual, and take out the old cartridge.
3. Rinse out any debris in the bottom of the tank.
4. Inspect the tank O-ring and replace it if it's flattened or cracked. Find replacements in O-Rings & Gaskets.
5. Seat the new cartridge so it sits squarely on its seats at both ends.
6. Reinstall the lid and clamp securely, open the valves, and start the pump with the air relief valve open until water flows from it.
7. Note the new clean pressure reading. That's your baseline for knowing when to clean next.

Safety note: Filter lids and clamps hold pressure. Always release pressure before opening the tank, and stand clear of the lid when starting the pump. Replace a clamp, lid, or pressure gauge that's damaged; see Filter Parts & Accessories.

Tips to make cartridges last longer

• Clean when pressure rises about 8 to 10 PSI above your clean reading, or as your filter's manual recommends, rather than on a fixed schedule.
• Keep a second set of cartridges so one set can dry fully while the other is in use.
• Keep your water balanced. Scaling water and oils from lotions shorten cartridge life.
• Don't use a pressure washer on the pleats. It can damage the fabric.

If you're replacing the whole filter, see Choosing the Right Filter and our Pool Filters collection.

Have your measurements but still aren't sure? Use the chat on this page or reach us through our contact page with your filter model or cartridge measurements, and we'll help you find a match.