Pool filtration

Over 20+ years of service, we have seen hundreds of errors in swimming pool system technology, but if you trace the cause, these errors almost always started with one simple phrase: "Can it be cheaper?"

To finally clarify the matter, we will explain how a filter should be selected for each specific pool. And — yes, why for us and companies that are responsible for the quality of pool water, it is almost always more expensive 🙂

Filtration Basics

Medium and large pools primarily use mechanical filtration tanks, most often with sand or glass media. There are also diatomaceous earth filters — they filter even the finest particles but are more demanding in terms of operating conditions.

Glass vs. Sand Media

• Sand media — classic, effectively traps large and medium-sized contaminants, affordable and relatively cheaper.

• Glass media — has a smooth surface, lasts longer, and traps fine particles better; it clogs less than sand. This means backwashing is needed less frequently, and the filter works more efficiently with the same bed thickness.

Diatomaceous Earth

• Diatomaceous earth is a natural silica powder derived from the fossilized remains of diatoms. It has ultrafine pores capable of retaining even microscopic contaminants that sand or glass cannot trap.

• Advantage — ultrafine filtration, minimal water turbidity.

• Disadvantage — requires special piping, close attention to water chemical balance, and regular backwashing, because any chemical fluctuation or pressure change in the system can quickly damage the filter.

Why are sand and glass popular for large facilities?

So, sand and glass are popular for large facilities not by chance: they are simple to operate and maintain, handle large volumes of water well without the need for complex pumps or additional devices, while the media and spare parts are affordable, and personnel requirements are minimal.

Filtration Bed Height and Turnover Rate

The desired media height for sand filters is 100-120 cm. This is important because it is at this thickness that the sand/glass layer truly has enough time to "do its job" at the calculated flow rate through the filter.

For commercial facilities, it is desirable to use two or more filters, and pumps are also duplicated – so that if one breaks down, the pool does not stop operating.

Tanks are chosen with sufficient capacity so that all the water in the pool can pass through the system the required number of times per day; we most often aim for six or more times. This is the norm that guarantees 100% filtration of the pool's water volume, ensuring safety and cleanliness.

Filtration Turnover Rate for Special Pools

• Children's pools — every 2 hours, as children are more prone to bacterial contamination.

• Infant pools — every 30 minutes, water must be as clean as possible.

• Hydro-massage pools — every 15 minutes, because due to high aeration and temperature, water quickly becomes contaminated and loses its sanitary quality.

Tank Bodies and Nozzles

• Tank bodies come in: wound, composite, and stainless steel.

• The bottom part of the tank for water intake or backwash supply has either a "Christmas tree" manifold or nozzles.

• Nozzles are more efficient because they distribute flow evenly and reduce "dead zones," but such tanks are more expensive.

• Christmas tree manifold — simpler, cheaper, but slightly less effective.

Now that we've covered the basics of tanks, let's talk about the main mistakes we see on sites.

Common On-Site Mistakes

❌ Filter flow rates do not match water volumes
The answer often lies with unscrupulous sellers who list backwash rates, not filtration rates, in their catalogs.

For example: a Ø650 filter has an area of 0.33 m² and supposedly "passes" 16–17 m³/h. But this is only for backwashing. The actual speed for effective filtration is 6–7 m³/h, so if a large tank and powerful pump are not used, the filtration quality may be insufficient despite the number of filtration cycles.

❌ Incorrect pipe plumbing
A non-obvious problem that hinders proper filtration even when the correct tanks and pumps are installed. Each pipe diameter has its actual flow capacity, and ironically – "classic" 50 mm or 63 mm may often be insufficient. Imagine that the calculated water speed requires a Ø75 mm pipe, but a Ø50 mm pipe is installed instead.

• Cross-sectional area of a Ø50 mm pipe = π × (0.025²) ≈ 0.00196 m²

• Cross-sectional area of a Ø75 mm pipe = π × (0.0375²) ≈ 0.00442 m²

• Ratio = 0.00442 / 0.00196 ≈ 2.25

This means the actual flow capacity drops by more than half. The customer sees the figure "16–17 m³/h," but in reality, only 6–7 m³/h passes through the narrow pipe. This is one of the most common reasons why pool water is not filtered effectively.

❌ Poorly placed suction and return fittings
We have been and will remain advocates of overflow pools, as most contaminants are on the water's surface. However, if for some reason an overflow system is not feasible, ensure that the skimmer placement allows for uniform water intake from the entire pool area, and that the return jets effectively mix the water and direct it towards the skimmers or overflow.

Conclusion

We do not compromise. We explain why you cannot save on pipe diameter, and we select filters for a specific volume and type of pool, not "by eye."

Brand-name Water World Window tanks are manufactured in Turkey specifically to our requirements — with diameters from 350 to 2000 mm, and each is inspected before installation.

We do not allow you to save at the start, but we save your money and nerves in the future, because filtration is not just about water purification, but the foundation of the entire pool's longevity.