What a range, rather than a number, describes
A range of grain diameters, and — where the maker gives it — a grading, which describes how tightly the grains cluster inside that range. Both are measurable properties of a sack of media and both are honestly published by most of the shelf.
Where EN 12904 is cited, rather more is fixed: the standard covers size distribution, silica content and acid solubility, which together decide whether the media survives contact with pool chemistry.
Why it is not a fineness in microns
It does not promise a filtration fineness in microns. What a bed catches depends on grain size, bed depth, flow rate and how long since it was last backwashed — four variables, of which grain size is one.
It does not promise a bed life. Sand is commonly replaced every few seasons; glass is claimed to last longer. Both claims are the maker’s, and both are reported as such.
And it does not promise a charge weight. That belongs to the filter, not the media, and the two are published separately for a reason: a tank takes what it takes.
What the filter publishes, and what the media does
Charge weight, in kilograms, which the filter’s own documentation states. Tank diameter, because it sets both the charge and the flow the bed can take. Stated fineness in microns where a maker publishes one, kept as a claim with its source. And, on glass, the origin of the glass, which several makers publish and which is the closest thing the shelf has to a provenance.
Sand, glass, and the tank that takes them
Filter sand and filter glass, where the range is the first line. Sand filter systems, where the charge the tank takes is printed alongside the flow — because a filter bought without its media is a filter that does nothing on the day it arrives, and that is one of the second purchases this site adds back to a price.
What readers keep writing in to ask
Is finer always better?
Finer media catch smaller particles and also block sooner, which raises pressure and shortens the interval between backwashes. The trade settles on 0.4–0.8 mm because it is a working compromise, and a maker offering a finer grade usually says which layer of the bed it is meant for.
How much glass replaces how much sand?
Glass is less dense, so a charge is normally smaller by weight than the sand it replaces — makers commonly state a figure around 20 % less. The page prints the maker’s own comparison where one is given, because the ratio differs between products.
Does glass filter finer than sand?
Manufacturers claim so, often quoting a figure in microns. It is reported here as their claim with the figure they gave. What is not in dispute is that glass does not cement into channels the way old sand can, which is the practical reason most of the claimed bed life comes from.
What is EN 12904?
A European standard for silica sand and gravel used in water treatment, covering grain size distribution, purity and acid solubility. Some pool sands cite it and some do not; where a product cites it, the page says so, and where it does not, the page does not imply it.
Last reviewed 21 September 2026