Salt Water Pool Filter Definitions And Glossary

Salt Water Pool Filter Definitions And Glossary

The filtration system of your pool is an important aspect to keep the water clean for swimming. Salt water pool owners often wonder if they can use the exact same filtration systems that other pools use and the answer is yes. We’ll talk about that more in detail below.

But you’re probably going to come across many words and phrases with the word filter in it and wonder what’s what. You’ll find that words like filter or pool filter are around a fair bit interchangeably so it can get confusing and you might wonder exactly what is being discussed.

Let’s take a closer look at pool filter definitions for your salt water pool and what each means.

Important Salt Water Pool Filter Terms


The filter is the actual system itself, the filtration unit and method used to clean your pool. There are three types of filter systems that you can use for a pool including a salt water pool: Sand filter, cartridge filter, and D.E. filter.

In general terms, pool water is sucked through the side skimmer at the side of the pool and main drain at the bottom of the pool by the pump and is drawn through the piping back through the filtration system to filter out particles, is chlorinated through the salt chlorination system and then returned to the pool.

So when you hear or read about a pool filter, you’re probably talking about the actual physical filtration system in general.


When you hear or read about washing your filters, rinsing your filters and things of that nature, they’re actually referring to the medium inside the filtration unit or system itself. A cartridge filtration system uses cartridges (pleated drums) that sit inside the actual filtration unit to collect dirt and debris that passes through it. The cartridges hold onto the debris and prevent it from reentering the pool. Over time the cartridges need to be rinsed to remove the collected dirt similar to how you’d clean out a vacuum cleaner filter from time to time.

A sand and D.E. filter needs to be backwashed which involves running pool water through the sand and D.E. medium to clean it out.

Filter area

Different filtration products and systems are rated at being able to handle a certain sized pool area. So the bigger the pool (the more water volume) the larger capacity filtration system you will require.

Tip: When choosing a filtration system for your pool you are better with one that is slightly bigger than needed than too small. A rule of thumb is to pick a filtration system that has 1 square foot per 10,000 gallons pool capacity.

Filter cartridge

Washing a salt water pool cartridge filter medium.
Washing pool filter cartridges is required from time to time to remove the debris that gets collected in the pleating.

A filter cartridge is the filter medium – the actual filtration device – that sits inside the filter housing to collect debris and hold onto it to prevent it from reentering the pool. Most cartridges are round and have a solid plastic base with soft vinyl-like pleated ribs that collect dirt and other contaminants.

When new, the cartridges are a clean white color and the pleating is very tight and straight. Over time it will turn gray with dirt and the pleating will get loose and out of alignment (see pic above) which indicates you’re getting closer to having to replace them.

Filter aid

You can help your filtration system work better by adding a filter aid of some kind, typically in the form of a liquid. It may be called a clarifier which is a blue liquid that you squirt directly into the pool water that eventually makes its way into the filter and helps your filtration system trap small particles that it may otherwise be unable to filter out.

The clarifier effectively helps to clump up smaller particles of debris into bigger ones so when they travel though the filter they are more likely to get stuck on the medium and remain in your system rather than going back out into the pool water.

Filter cleaner

A filter cleaner is a concentrated liquid that can be added to water in a large bucket to soak your filter cartridges in to remove oils and other debris that simply hosing them off won’t.

In my experience if you have a cartridge filtration system, using a filter cleaner perhaps once per season and soaking your cartridges over night can help to extend their life and also enable them to work more efficiently.

Filter cycle

Can refer to the amount of time you run the filtration system each day which in turn is determined by how long you run your pump. When the pump is running, water is being filtered and when the pump is off no water is being filtered.

Filter cycle may also refer to the cycle of your sand filter if you use one. Sand filters require regular backwashing to clean them out. This involves draining water from your pool through the sand to wash out all the contaminants and debris that have been collected by the filtration system since the last backwash. Backwashing typically occurs when the pressure gauge of your filter has reached a certain level which indicates that enough debris has collected in the sand that it needs to be rinsed out.

Filter element

The actual device that is used within the filtration system to filter the water. In a sand filter, the element is sand. In a cartridge filter, the element are the cartridges. In a D.E. filter, the element is the diatomaceous earth (D.E.).

So it’s just another general name for the actual substance that actually filters the water.

Filter medium

See filter element.

Filter powder

Also known as diatomaceous earth which is the medium used in a D.E. filter. The most expensive type of filter to purchase, a D.E. filtration system is also widely considered to offer the best filtration in terms of being able to filter out smaller particles than either a cartridge filter (second place) and sand filter (third place).

Several downsides exist with D.E. filters:

  • They require backwashing like sand filters which takes time and uses water.
  • The filter grade D.E. medium is hazardous so it has to carefully handled and not accidentally inhaled.
  • Some jurisdictions don’t allow you to backwash D.E. filter water into the local sewage system.

Filter sand

How full should my pool sand filter be?
Sand filters use special pool grade filter sand that is very different from that used in a sand box.

Filter sand is used with a sand filter. The sand used in your sand filter is typically specified by the filtration system manufacturer in terms of how much and what type. Filter sand for a pool is not the same nor is it substitutable with sand that you’d use in a kids’ sandbox as the two types are very different.

While your filter manufacturer may specify the specific type to be used, the common style of pool sand is No. 20 grade silica sand. Sand has to balance between being not too fine or too soft because either scenario can clog the system.

Pool filter sand is usually replaced every 3 – 5 years or as needed or as specified by your filter manufacturer.

Filtration rate

The filtration rate is the rate at which water passes through your filtration system and is expressed in gallons per minute (GPM) or liters per minute depending on where you live. The filtration rate is dependent on your pump capacity. Some pumps are one speed whereas you can also purchase multi-speed or dual speed pumps which can be run at differing speeds that will affect flow rate.


A salt water pool can use the exact same filtration options as other pools, namely a cartridge filter, sand filter or D.E. filter.

While a sand filter is the cheapest version to buy, it does require backwashing which involves draining significant (several hundred gallons) of water each time to properly rinse the sand out. A cartridge filter is the next price point and the cartridges that it uses will need to be replaced every 3 – 5 years. The most expensive filtration system to purchase is the D.E. filtration system which also needs to be backwashed.

It’s your choice as to what you get but if you’re looking for a filter option that is reasonably priced, works well and generally has lower maintenance, consider a cartridge filter system.

Carl Mueller

I bought a home with a salt water pool in 2006 and soon realized the benefits over traditional chlorinated pools. On this website I'll discuss all the tips and tricks I've learned over the years. I'll also help you troubleshoot various problems with pools in general and ones specific to salt water pools that I've experienced personally!

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