Frequently Asked Questions

How often do I need to clean my cartridge filter?

Because a filter is designed to collect unwanted particles, debris, oils, soaps etc, it will need to be cleaned periodically. Basically the more you use your spa or pool, the more often you have to clean the filter cartridge. From very high usage (every 2-3 weeks) to low usage (every 2 months).

A blocked cartridge can put undue pressure on your pump and motor and decrease the life of these parts.

Please see maintenance section for further advice on cleaning.

How long will my filter cartridge last?

Magnum filter cartridges do not have a defined termination point, but over a period of time your cartridge will gradually block up and will need replacing.

Filter Cartridges are designed to take particles, sediment and oils etc out of water. If they block up, it means that they are doing the job correctly.

The cleaning cycle time and lifespan is a direct result of the quality of the water passing through the filter.

If you have a new concrete pool or paving area, the life of the filter cartridge will be reduced due to the fine concrete dust blocking the material.

There are three factors in determining whether you cartridge needs replacing: 

  1. The cartridge gets blocked quickly, and you have to clean your cartridge more often.
  2. Restricted water flow and high differential pressure (differential pressure is the difference between the pressure coming in and the pressure going out).
  3. A cracked or damaged cartridge (this is very rare, and is usually caused by incorrect installation or high differential pressure).

In a spa or pool with very high usage you will need to change the cartridge within a year, but normally between 18 months and 2 years.



Why is the endcap cracked?

This is very rare. but if the filter cartridge is very old and dirty, it needs to be replaced.

If the filter cartridge is fairly new, then the filter housing or skimmer box could be plumbed backwards.  Simply put, the inlet and outlet on the filter housing or skimmer box were reversed during installation, which means the water flow is going through the cartridge filter ‘inside out’ rather than ‘outside in’.

Signs a cartridge is plumbed backwards:

- A circular crack around the centre hole.

- Cracks in the endcap from the centre hole to the outside of the cartridge.

- The pleats appear to be rounded and puffy, rather than sharp.

- Bands broken or damaged.

- The inside of the cartridge (down the centre core) will be dirty.

Our advice is to immediately contact either your service technician who installed the filter housing in the case of a spa, the retailer you purchased it from.

 Cracked SQ50 clipped rev 1RD50 Reverse Plumb clipped rev 1plumbed backwards 3 clear cut2 clipped rev 1RD50 Reverse Plumb 3 clipped rev 1


In the dimension chart, there are two cartridges with the same dimensions, which one do I need?

Some cartridges are the same size but the difference is the amount of filter material (number of pleats). Manufacturers of filter housings do this so they can use the same housing for different size pools or spas. If the filter housing does not stipulate the type of cartridge (e.g. 50sq ft or 75sq ft) then please contact the manufacturer or installer of the filter housing. If this can not be done, it is better to over spec than under spec, (e.g. 75 instead of 50). If it has more square footage than it needs, it will normally last longer. 


Why can’t I find my cartridge filter on you dimension chart?

There are many hundreds of different kinds of cartridge filters. If you can’t find one that is close to your dimensions, please contact us –

It’s more than likely we do or can make the cartridge you are after, as we add to our range on a regular basis.


Can I use a Flocculant with Cartridge Filters?

Most flocs are incompatible with cartridge filters. 

Do not use a unless you have a valve to allow pool water to waste, if not, remove the cartridge then vacuum to waste. If no waste valve is fitted, then a light clarifier may be used but the cartridge should be cleaned frequently to avoid a build up of pressure.

Flocs prematurely block cartridge filters, so will void any warranty.