▷ 12 questions/answers on swimming pool filtration

The filtration speed of a swimming pool is calculated very simply. To have healthy water, all water must be filtered within 4 hours. The optimal flow rate for a swimming pool is therefore: Water volume in m³ / 4 (hours) = flow rate in m³/h.

If you are exposed to bad weather and there are many swimmers, you will have to take a slightly higher flow rate, adding a coefficient of 1.20 to this calculation.

I live in Burgundy and my pool is 32 m³, I need a filtration unit (filter + pump) with a flow rate of 8 m³/h. (32/4 = 8)

I live in PACA and the Mistral brings a lot of dirt into my 32 m³ pool. I need filtration with a flow rate of 9.6 or 10 m³/h. (8×1.20 = 9.6)

2. How long does the filtration of a swimming pool last?

To keep your water clean, healthy and crystal clear, you need to pay close attention to filtration time. The filtration time has nothing to do with the volume of water in the pool. This calculation is therefore valid for all swimming pools. The filtration time is equal to water temperature divided by 2.

To do this, measure the water temperature once a month and adjust the filter time accordingly. In very hot climates, be sure to monitor this time carefully and even increase it. Warm water requires more monitoring than cold water early in the season.

In May my pool is at 22°, I have to filter it 11 hours a day

In July my pool is at 27°, I have to filter it by 1.30pm. per day

Filtration does not have to be done in one piece. Divide the daily filtration time into 3 phases.

3. Which system offers the greatest filtration fineness?

There are 3 main types of filtration, all with advantages and disadvantages but also different fineness of filtration. A quick performance review:

Cartridge purifier: from 10am to 30pm micron
Sand filter
- Sable: 30-40 micron
- Glass : 15 micron
- Zeolite: 5 micron
Diatom filter: from 2 to 5 micron

As you can see, the solution that offers the best filtration fineness is the diatomaceous earth filter. It is less common and more expensive. Instead, I advise you to opt for a sand filter and put glass or zeolite inside. Note: Glass is more expensive than sand but is more durable (9 years compared to 3-5 years for sand).

4. What is the least expensive filter system?

The finer the filtration system offers, the more expensive it will be.

Cartridge purifier

The device is cheap to buy.

Replacing cartridges regularly can quickly add up to your bill.

Sand filter

It is more expensive than the cartridge purifier but has excellent value for money in relation to its performance and durability.

Depending on the type of filter media used, this may be an initial investment. However, it remains moderately expensive compared to their lifespan of 3 to 9 years.

Diatom

Very expensive device, due to its performance.

Quite expensive because the renewal of the diatoms is regular.

5. Is filtration alone enough to rid water of impurities?

Filtration allows you to clean and purify water from microorganisms present in the water:

Microorganisms carried by humans: sweat, secretions, cosmetic products, dead cells, germs, etc.
Microorganisms brought by nature: leaves, insects, dust, pollen, etc.

Once the water has been filtered, these elements will pass through the sieves (skimmer basket for large waste and pre-filter basket for medium waste) then into the filter which will retain the impurities (particle filter medium).

Filtration prevents the water from stagnating and developing algae, leaving it clean and healthy but has no disinfectant action. Does not kill bacteria and viruses. This is why it is very important to disinfect the water to completely clean it of these microorganisms. >> Read our article on this topic

Furthermore, to preserve it, it must also be cleaned by hand: vacuum the bottom, brush the walls and the waterline. >> Read our article on this topic.

6. Is it possible to lengthen the filtration tubes?

If you want to place your filter in a specific location and the length of the tubes that come with the filter are not long enough, you have probably thought about lengthening the tubes. This is not really recommended because it will slow down the filtration flow and be less effective. If possible, build according to the length of the expected pipes.

However, if absolutely necessary, reduce the diameter of the pipes to increase the flow rate using an adapter and install pipes of the desired length.

Focus on cartridge purifiers

7. When to change the filter cartridge?

The filter cartridge of a cartridge purifier has a cylindrical shape, composed of plant fibers or synthetic materials, folded into a star. It is these folds that retain impurities and define the fineness of the filtration.

Like a coffee filter, impurities stick to the fiber. After a certain time, the fibers become damaged and no longer perform their filtration function. It’s time to change the cartridge!

At the beginning of the season, when the water is still fresh and there are not many swimmers, it is possible to change it every time 3 – 4 weeks. In high season, when the water is around 25-32° and the children are having fun in the pool, it is necessary to carefully monitor the state of the cartridge and replace it every 2 weeks.

8.How to extend the life of the filter cartridge?

To consume fewer cartridges and ensure good water filtration, it is necessary to clean the cartridge. Cleaning consists of rinsing with a jet of clean water. This approximately twice a week.

Focus on sand filters

9. How often should you clean the sand filter?

To maintain its effectiveness in terms of filtration, the sand must be clean. To do this, you need to run backwashing of the filter (the 6-way valve has a “backwash” phase). This backwash should be done every 3 weeks/1 month.

Some filters are equipped with a gauge. It’s even easier to know when to clean it! As soon as the needle is on the red, the sand is too dirty.

10. When to change the filter media of your sand filter?

Sand: every 3-5 years
Zeolite: every 3-5 years
Filter glass: every 9 years

11. How much filter material should you put in your sand filter?

Depending on the diameter of the tank the quantity will not be the same. If the supplier indicates the quantity on the product, it’s easy :)!

Otherwise there is a general rule : the tank must be filled up to 3/4 about sable.
When using other filter media, a filling of 55% zeolite or filter glass.

For an aquarium that requires 50 kg of sand, you will need approximately 40 kg of zeolite or filter glass.

12. Why not use a flocculant?

To improve the filtration fineness of sand filters it is possible to add a flocculant. The water will be clearer and better filtered.

Please note that the flocculant should only be used for sand filters containing sand!

To improve the filtration fineness of cartridge purifiers it is possible to use a clarifier, which will have the same effect, without damaging the filter.