Sand vs quartz pool filter — which filters better?

First, a correction that resolves half the confusion: "sand" and "quartz" filters are the same thing. The media in a sand filter is quartz sand — these are not two types of filters, but two names for the same device. The real decision you are making is the second one: quartz sand or activated glass as a filler. The sand retains particles of 30–60 microns, glass according to the manufacturer's declarations until 5 microns, and lasts up to three times longer.

Below is a breakdown explaining why the declared flow rate on a filter is not the operating point but the maximum, how much media is actually needed, and when replacing sand with glass makes sense and when it's a waste of money. If you're putting together an entire engine room, start with the guide through swimming pool technology and equipment.

Where does the "sandstone vs quartz" confusion come from?

The confusion comes from advertising. Sellers sometimes write "quartz filter" to emphasize the quality of the filling, giving the impression that there is a third type of filter. There is none. In practice, two types of filters are used in home pools:

• Sand filter — a vessel with a medium through which water passes from top to bottom. The medium is quartz sand or activated glass. It is washed countercurrently (backwashing).
• Cartridge filter — an insole made of pleated material that can be removed and washed or replaced. It filters finer, but does not backwash.

We do sand filters in the engine room, so this article is about them. This is not because the cartridge is bad — it's because the sand filter is washed with one turn of the valve, without removing it and manually rinsing it, which significantly changes how much the owner actually engages with the pool throughout the season.

The declared filter flow rate is the maximum, not the operating point.

This is the most important figure in the entire text and is almost never explained. The filtration rate is measured in meters per hour and is obtained by dividing the flow rate by the filter area. According to data provided by pool-magazin.com, the limits are:

• private pools: maximum 50 m/h
• public freshwater pools (DIN 19643): maximum 30 m/h
• public pools with sea or salt water: maximum 20 m/h

The same source explicitly states that the quality of the filtrate decreases as the speed increases. Now look at what the manufacturers actually declare:

Each of them is declared practically exactly at a private maximum of 50 m/h. This is not a scam — that is how filters are declared throughout the industry. But it means that a filter that says “9 m³/h” is operating at the upper limit of what is allowed, without any reserve. If you want the quality of the filtrate that the regulations require for public pools, you can drive that same filter on 5.9 m³/h.

Calculation: area = π × (diameter ÷ 2)². For D500 it is π × 0.25² = 0.196 m². Speed = 9 ÷ 0.196 = 45.9 m/h.

Quartz sand or activated glass?

This is an actual choice. Both options go into the same filter and are changed in the same way.

Arithmetic is fairer than it seems at first glance. Glass is in the bag 2.2 times more expensive, but it lasts up to three times longer and requires less weight. Over the life of the filling, it comes out to be about the same or slightly cheaper — and you get finer filtration and less water used in washing. Read the manufacturer's instructions for the number of bags per filter, as it depends on the diameter of the container.

What granulation and how much media?

According to DIN EN 12904, two granulations are used in practice: 0.4–0.8 mm and 0.7–1.2 mmFiner ones retain smaller particles, coarser ones provide less resistance and are easier to wash.

In larger filters, the media is arranged in layers — a coarser layer at the bottom around the collection branches, a finer layer above it. That is why coarser granulations are also available, such as 1.0–3.0 mm and 3.0–5.0 mm: they are not "worse sand" but the lower, supporting layer. For the height of the embankment, the source states the guidelines 80 cm, but take the specific height and distribution of layers from your filter's instructions.

Do not improvise with building sand. The filtration medium is washed, calibrated and declared by granulation — construction sand has uncalibrated particles that either pass through the collection branches or compact into an impermeable crust.

What size filter for which pool?

You choose a filter based on the pump's flow rate, and a pump based on the pool's volume. The order is important: first calculate the required flow rate, then choose a filter that can handle it with a margin, and only then a pump that will not exceed it.

Prices are from our offer and are subject to change. For the 8 × 4 m pool, we deliberately skipped the D500 even though its declared flow of 9 m³/h is not far from the required 12 — because the filter would work above the declaration. The entire offer is in category Engine room ▸ Filters.

Filter washing: when, how long and how much water it takes

The filter is washed countercurrently — the water flows in the opposite direction, lifting the media and carrying the accumulated dirt into the drain. According to the source, the washing speed is 45–50 mph, common frequency once a week, and it lasts 3–5 minutes, or until the water in the inspection window becomes clear.

But the calendar is not the best indicator — The pressure gauge isWhen the pressure increases by about 0.3–0.5 bar above the value the filter shows with clean media, it is time to wash. Record this clean value immediately after the first wash; without it you will not know whether 1.4 bar is normal for your system or a sign of a problem.

After washing, a short rinse is mandatory (rinse) of 20–30 seconds before returning to filtration. Without this, the cloudy water from the collection branches goes straight back into the pool and the owner concludes that washing has made matters worse.

Frequently asked questions

Which filter purifies better?

The question is actually which medium purifies better, because the filter is the same. Quartz sand retains particles of 30–60 microns in size, and activated glass, according to the manufacturer's declarations, up to 5 microns. Glass therefore filters finer, lasts up to three times longer and requires less frequent washing. Note: the figure of 5 microns is the manufacturer's declaration, and glass poured into a sand filter still works in this, structurally less efficient version.

Should sand be replaced with glass?

It makes sense when the sand is already nearing the end of its life, when the filter is being washed more often than before, or when it is difficult to keep the water clear with proper treatment. It makes no sense as a first solution if the problem is elsewhere — an oversized pump, a filter that is too small, or disinfection that is too weak are not fixed by changing the media. Glass is about 2.2 times more expensive per bag, but over its lifetime it comes out to be about the same.

How often do you clean the filter?

As an indication, once a week, for 3–5 minutes, or until the water in the window becomes clear. A more accurate indicator than a calendar is a pressure gauge: wash when the pressure increases by 0.3–0.5 bar above the value with clean media. After washing, let the rinse run for 20–30 seconds before returning to filtration.

Next step

Measure two things before you order anything: the volume of your pool and the diameter of your existing filter. From the volume you get the required flow rate, from the diameter you get the filtration speed at which your system is currently operating. If this speed exceeds 50 m/h, the problem is not the media but the sizing — and replacing sand with glass will not help here.

You can view filters, quartz sand and active glass in category Engine room ▸ FiltersIf you are not sure what suits you, Please let us know the filter diameter, pump flow rate and pool volume. — we typically respond to inquiries within 24 hours and will also tell you when the answer is that your existing system is working just fine.