Cartridge filter technology was invented in the mid-1960s. Despite the system’s availability for around half a decade, it has only taken precedence over the other filtration technologies relatively recently.

First appearing in oil filter configurations, Cartridge filters have larger surface areas compared to sand filters. This enables cartridge filters to operate for longer periods, as obstructions occur less with bigger filter surfaces. Cartridge filter systems also permit better water flow – thus, placing less strain on the filter pump. These types of filters are also easiest to clean by using a flow of high-pressure water from a hose. Cartridge filters require cleaning around four to eight times a year. The filter will primarily catch larger debris while the cartridge is clean. Once the filter’s pores become clogged with larger particles, the buildup will allow the filter to trap smaller debris.

The filters are actually made of polyester or some other material that can provide a superfine filtering surface. The pleats are the key to the filter’s operation. The tight pleats, or folds, allow for a large amount of material to be used in a small container. The more material used, the larger the surface area available to capture unwanted dirt or debris in the water. The fabric catches and holds the impurities until you clean or replace the filter. There 3 parts to a cartridge filter construction,end caps (made of plastic) core structure to provide strength (most often PVC) and the pleated media (most often polyester (Remay being the dominant brand). Cartridges are high efficiency depth style filters constructed of polypropylene. Constructed of polypropylene,[3] with a continuously graded fixed pore structure, these cartridges provide pre- and final filtration within the same cartridge resulting in lower overall filtration and disposal cost.

Two methods are used in Hot Tubs with respect to cartridge filters, pressurized canisters,in which the spa filter is not visible when in use, and secondly flow through systems, which are visible when in use and often the spa has 1-5 filter cartridges in this design. Flow through filter system in spas and hot tubs are the preferred method of design today for all major hot tub brands.

The Hot Tub cartridge can filter out anything down to about 5 to 10 micrometres in size. A grain of table salt is about 90 micrometres; anything below about 35 micrometres is invisible to the naked eye. It is important to remember that with any filter a small amount of dirt actually aids the filtering process. In most areas cartridge filters are less expensive than diatomaceous earth filters but cost more than sand filters. However cartridge filters are more popular because of the minimal maintenance involved. Some families will find it sufficient to simply hose off the cartridge filter a few times during swimming season to keep them working properly. Others may need to soak the filters in detergent or replace them. In any case, maintenance takes only a few minutes to the filtration system in top shape.

There are more than 500 shapes and sizes of HotTub filter cartridges in use today. Most major Hot Tub brands have designed their own yet all of them are available from aftermarket sources.
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