Glass filter media
Also called: recycled glass media, filter glass, crushed glass media.
Glass filter media is crushed, sized recycled glass that drops into the same tank as filter sand and does the same job. Compared with #20 silica sand, glass filters finer, lasts longer at about 5–7+ years, and weighs about 20% less for the same job.
Why it matters
A sand filter is really a tank you fill with a filtering medium, and sand is only one option. Glass has a slight negative surface charge that helps grab fine particles and resists the channeling that lets dirty water slip through. It costs more up front. Treat the fineness claim with care: the micron figures quoted for glass are claims about the category or the maker's own claim, not a test. Glass replaces sand at about 80% by weight. No medium fixes chemistry: a filter polishes water that is already balanced and properly chlorinated. Wear an N95 or better while you pour, because glass throws dust too.
In numbers
Vitroclean, a recycled-glass media maker, says 40 lbs of Vitroclean replaces 50 lbs. of sand, so multiply your filter's sand weight by 0.8: a tank that takes 150 lb of sand wants about 120 lb of glass.