Filter of choice for most spas and many smaller above ground pools, the cartridge filter is enjoying a resurgence in popularity. The cartridge filter element, an aquatic version of the pleated air filter in your car, traps dirt and particles of 25 - 100 microns in size. To clean the filter, the cartridge is removed from the tank and hosed thoroughly, top to bottom, with a garden hose. This is done as necessary to remove dirt when the pressure gauge rises 8 - 10 lbs. above its clean reading.

Today's filter cartridges are made from spun polyester, and the brand Reemay™ is the brand of choice. Reemay is pleated and wrapped around a heavy plastic or pvc core that allows water to flow from the outside of the cartridge to the center core. Pool filter cartridges are bound on each end with a heavy type of rubbery plastic that is melted or fused to the ends of the rolled up pleats and the inner core.

Unicel is a popular manufacturer of replacement cartridges for most of the pool equipment manufacturers. Other brands have gained some market share in recent years, notably Filbur and Pleatco. Pleatco has a unique core design, but they mostly use the same materials and methods in manufacture. OEM cartridges are also available, but be prepared to pay a premium for the brand name!

The cartridge should be replaced every 3 - 5 yrs., depending on the work it was asked to do. If the filter was a bit undersized, and has some algae every year and lots of tree debris, etc. then it may last only 1 - 2 years. Nicely sized cartridge filters can operate for 6 months between cleanings and get more than 5 yrs. from the cartridges.

How often it needs cleaning depends on filter size, and dirt load in the pool. I have worked with undersized cartridge pool filters from the 80’s that require 1-2 cleanings per month, and also had the pleasure of working with large new filters, that need cleaning only 1-2 times per year. The best indicator is the pressure gauge; when it rises 8-10 lbs above the clean pressure, or flow rate is noticeably diminished, it’s time to open up the filter and hose down the cartridge.

There is very little required with maintaining a cartridge pool filter. Without a filter valve, and very few parts other than the filter cartridge, there is little to go wrong. Keep the belly band o-ring clean and lubricated, and replace the filter cartridge after 10-15 cleanings. Other than replacement of damaged filter parts, there is little other maintenance needed.

A trick question. There is no backwash valve on a cartridge filter because cartridge filters aren't built for backwards flow. Instead, the pump is shut off, air bleeder opened to drain the tank, lid removed, cartridge(s) removed, hosed thoroughly top to bottom, and replaced. It's a bit of a pain to do, but hopefully the filter is sized so that it's a once or twice per year job. Another advantage is that cartridge cleaning a cartridge filter uses so much less water than backwashing, saving thousands of gallons per year.

Soaking the cartridge in a TSP (trisodium-phosphate) or similar solution prior to hosing will improve your cleaning. Do not use TSP if you utilize Baquacil or Soft Swim for sanitation. You can also use one of the many chemicals labeled pool filter cleaner, but just be sure that it states that it is suitable for cartridge pool filters.

Yes, if possible, after cleaning your cartridge, place in a warm spot to dry completely for 24 hours. This allows any microscopic organisms to dehydrate and expire. It is best to have a second set of filter cartridges, to replace while you store a second set. In most cases, you can operate a cartridge pool filter without the cartridge inside the tank, if needed to maintain circulation while a cartridge dries. To do so, be sure all internal parts are removed and that the tank is reassembled tightly.

If you have debris bypassing the filter cartridge, then dirt and particulate matter is probably also getting by the filter. Cartridge filters are designed to force the water through the pleats, and as we know, water will always take the path of least resistance. Make sure that all internal parts such as baffles or diffusers are in place, if any, and that the cartridge is properly seated when reinstalling.

Poor sanitation, poor water balance, and poor circulation could be another cause, and it could have nothing to do with the filtering at all. It could also indicate a need to replace the cartridge, and as a filter ages, the length of time between necessary cleanings becomes shorter. Some filters are sized fine for good water conditions, and do well when water conditions are good, but try to clean up an algae bloom or cloudy water and they struggle. If this is you, look at the size of your filter, or the age of the cartridges. The filter may be undersized. Bigger is better with pool filters (but not with pool pumps)!

Use of a clarifier from Sea-Klear or Natural Chemistry is a great help to a cartridge filter. But many clarifiers are not suitable for cartridge pool filters and could damage the delicate fibers. I have heard that some people also increase a cartridge filter efficacy by adding a small amount (1 cup) of synthetic filter aid powder like Aqua-Perl. D.E. powder is not recommended by most manufacturers.

It depends on the time of year, air temperature and water temperature. Careful experimentation will show you when the water quality begins to suffer. Many people with smaller, older equipment (filter/ pump) run their systems 24 hours per day. The average (I would guess) would be about 12-16 hours. BUT! It depends on your filter and external variables. Undersized or Old Filter? High Pool Use? Large Debris Load? Heavy Sunlight or High Temperatures? Any of these factors call for extra filtering, and extra chemicals. If you're too frugal with the electricity or if you forget to turn the pump back on - you likely pay more in chemical costs.

Most cartridge filters have a belly band clamp with a large o-ring between tank halves. The clamp band may be spun-off, no tools required or you may need a socket set or large open end wrench. The o-ring between the tank and the lid can become distended or flattened and may need to be replaced if water is dripping from the center clamp. Clean and Lubricate the o-ring annually, and always make sure to re-secure the lid properly after removing. Caution: Do Not remove the center clamp while the pump is running, and without first releasing pressure inside the tank.

Most cartridge filters have a drain, some smaller ones do not. You may experience leaking around the drain assembly, cap or plug. Teflon tape on the threads usually helps, and can also be used around the air bleeder / pressure gauge assembly to keep it from leaking. Air bleeders may also have a small o-ring on the part that is twisted to allow air to escape.

Most polymer filter tanks will not split or crack, but needless to say, if they do, they need to be replaced. Likewise with older (1970-90) stainless steel clam shell type filters from Purex or Sta-Rite or Wet Institute, etc.. If these develop pinholes in the stainless steel filter tank, replace the entire filter. These older filter models are no longer considered safe, and tank halves are no longer available.

Filter Cartridge Replacement:
Right off the shelf for $40 - $90, although some large cartridges can cost several hundred dollars. No professional labor needed, they are installed easily by shutting off the filter pump, opening the air bleeder, and removing the filter top or lid.

Filter cartridges that fit your filter may be available with options for filter surface area. By increasing the number of pleats, more surface area can be added to a cartridge of the same dimensions. In addition to more filter area, your filter size or dims may also be available in a blue antimicrobial version.

Filter cartridges for pools and spas are manufactured by 3 main companies in the U.S. – Filbur, Pleatco and Unicel. Chances are, each one of these manufacturers makes 1 or more replacement cartridges to fit your pool or spa filter. Less common or new filters may not be in production by all 3 firms. OEM (original equipment manufacturer) cartridges are also available, sold as cartridge filter parts. OEM cartridges may outlast a less expensive alternative cartridge, but over the long term, it likely will average out.

The differences between most filter cartridges are small, but a better cartridge would have an advantage in the areas of fabric weight and density, strength of endcaps and stability of the inner core. All 3 of the major filter cartridge makers compete fiercely with one another for sales, and although they do make a few grades of cartridges to meet certain price points, the quality is never in question, or they may lose some market share to the other guys.

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