What size pool filter do i need?

Friday, 26th Nov 2021 in Swimming Pool & Hot Tub Advice
What size pool filter do i need? | Blue Cube Direct

What size pool filter do I need?

Bigger is always better!

Choosing the right pool filter for your pool can make a world of difference to the overall functionality of your pool and the costs. A pool filter is one of the main components used in keeping your pool clean and safe. Your pool water flows from your pool through your filter where it is cleaned by removing tiny particles, these particles are measured in microns, the water then passes through your heating, pump and back into your pool.

Microns or micrometre is the measurement of tiny particles, it stands for one-millionth of a metre. For example, human hair is around 50 microns and bacteria are around 2 microns.

There are certain considerations to consider when choosing the right filter and the correct size pool filter.

Firstly, there are three different types of pool filters:

  • Sand/glass filters – Most commonly used to inground domestic pools
  • Cartridge filters – Used in above ground and smaller pools.
  • Diatomaceous earth filters – Mostly used in America.

Sand filters are the most common filters used in both domestic and commercial pools in the U.K. Pool water is drawn through the pipework into the filter tank where there is either sand or glass filter media, this media has rough edges which grabs particles which are 20 microns or larger and holds onto them, preventing them from re-entering the pool water. Over time the sand or glass is slowly eroded and becomes smooth and therefore can’t capture the particles at this point a media change is required, this usually takes 5-7 years.

Over time particles build up with the filter media, causing the flow of water to slow down and pressure to build up, when this happens the filter is no longer functioning properly, and this can put an extra strain on the system. When this happens a backwash is required, a backwash simply flushes water through the filter and out to waste, avoiding the pump, what this does is clean the filter media and remove the build-up of particles.

There 3 media types that can be used in sand filters:

  • Silica sand – Traditional and most common
  • Zeosand – Need half the amount, traps smaller particles, requires less backwashing, improves water quality, and has a similar life span to sand.
  • Glass – Use 20% less than sand, lasts up to 5 times as long as sand and traps particles as small as 5 microns.

If a filter removes dirt particles, you may be wondering why we still need to add chemicals, as previously mentioned, sand filters remove particles that are 20 microns or larger which means that particles 19 microns and smaller such as bacteria still get through and therefore need killing with sanitiser.

Cartridge filters are considered energy efficient and inexpensive; they also can capture smaller particles starting at 10 microns. They work by water flowing through pleated polyester which is in a cylindrical shape. Although it can capture smaller particles they are not designed for large quantities of water and therefore can not be used in most inground pools. They also require a little extra attention when it comes to cleaning, no simple backwashing, they must be removed, hosed down, sprayed with filter clean and regularly soaked to remove the build-up.

Diatomaceous Earth (D.E.) Filters are expensive and not commonly used in the U.K due to the expense. However, they can filter particles as small as 5 microns, the filter media is made of fossilised remains of tiny aquatic organisms called diatoms. D.E filters are also backwashed however more earth needs to be added after each wash. The earth needs to be disposed of properly as it can build up over time and clog drains.

Before you choose a filter, it is important to make sure you check what size pump you have and whether the pump is the correct size for your pool.

Oversizing a pool filter is unlikely to cause major issues but having a large pump and a small filter can cause an increase in wear and tear on your pump.

However, a small pump and large filter will reduce the amount of work the pump is needed to do.

A larger filter will mean less cleaning such as backwashing and due to slower pressure build ups, it will increase its life span as it must work less.

Key features of larger filters:

  • More time between backwashing
  • Greater filtration of the water
  • Longer lasting filter media
  • Longer filter cycles
  • Less backwashing

So how do you work out what size pool filter you need?

For example: 10 x 5 x 1.5 = 75 add 000 for litres = 75000

                       75,000 / 4          = 18750

This gives you the minimum flow of your filter

Firstly work out how many litres you have in your pool volume which you can do by multiplying the length x width x depth of your pool. Then divide this number by your desired turnover time which should be between 4-6 hours. To find your flow rate, divide your litres by turnover this will give you LPM.

Blue Cube Direct have over 15 years’ worth of pool filter experience, we are happy to advise and help you find the perfect filter for your needs.