Natural quartz sand
Natural quartz sand is available in various qualities and grain sizes.
Although quartz sand gets washed, it may contain pollutants. Please make sure that it complies with DIN 12904 (drinking water treatment) when you buy it.
The finer the grain size, the greater the surface area and thus the filtering properties, but the grain size depends on the filter system. Small grains may be flushed out, depending on the filter system. The best results are achieved with three layers of different grain sizes:
- Very coarse quartz sand with a grain size of 3-4 mm is recommended for the bottom layer.
- Somewhat finer quartz sand with a grain size of 2-3 mm is suitable for the middle layer.
- Very fine sand with a grain size between 0.4 mm and 2 mm achieves the best filtering result when it is in the top layer.
It is recommended to fill the filter system only approximately 50% with sand so that the backwashing and swirling of the sand work best. In addition, natural quartz sand should preferably be replaced every 2-3 years, as it tends to clump together and form channels, which considerably reduces the filter performance.
Frequent backwashing helps to keep the filter system running and to change the sand less frequently.
Advantages and disadvantages of quartz sand
The surface of quartz sand is rough and asymmetrical, what increases the filtering effect because suspended particles are retained more efficiently. The disadvantage, however, is that bacteria can also settle in the sand and form a biofilm that protects them from chemicals such as chlorine. In this biofilm, bacterias produce ammonium, which reacts with chlorine to form inorganic chloramines (mono-, di- and trichloramine). Trichloramine causes an unpleasant chlorine smell.
Zeolite
Zeolite is made from stones of volcanic origin and is a mineral powder used as a filter medium for sand filters. Zeolite can be used alone or mixed with sand or filter glass. It is recommended to fill the filter system only 50% to 60% with zeolite and to replace the filter medium every 7-8 years.
Advantages and disadvantages of zeolite
Zeolite offers an excellent filter fineness of 5 microns, which makes it a better performer than any other filter media.
Zeolite has the great advantage that it additionally stabilises the pH value and thus helps to reduce the consumption of pH-correcting agents. It also has the property of absorbing AOX (adsorbable organic halogens). Zeolite is much more expensive than sand but offers better performance.
Filter glass
Filter glass is also available in different grain sizes. The recommendations for quartz sand also apply to filter glass. The quality of the glass is determined by its surface structure and finishing. Dryden Aqua also offers a product called AFM (Activated Filter Material), which has a larger surface area and is negatively charged on top of it.
The molecular weight of the glass is smaller than that of quartz sand. Therefore less weight is needed for the same volume: approx. 20 kg of filter glass has the same volume as 25 kg of silica sand.
Advantages and disadvantages of filter glass
Due to the smooth surface, filter glass has a less effective filtering effect than quartz sand (I don't believe Dryden Aqua). Nevertheless, I agree that it is more difficult for bacteria to settle and there is less clogging and channel formation. It also needs to be replaced less often and thus saves costs.
Due to the lower weight of the filter glass grain compared to quartz sand, the former is stirred up and cleaned better during backwashing, but can be rinsed out sooner.
Conclusion
Quartz sand and filter glass have excellent filtering properties and both are very suitable for filtering pool water. Both products have advantages, but also disadvantages. So you have to decide for yourself which properties are more important to you.
I have decided to mix zeolite with filter glass in three layers.
