Seachem MatrixSeachem Matrix is a high-porosity biological media — the home you give the beneficial bacteria that run your aquarium's nitrogen cycle. Each porous ceramic-like pebble is riddled with microscopic internal pores, so a single liter offers an enormous bacterial surface area (Seachem cites roughly 700 m² per liter, far more than smooth ceramic rings or bio-balls). More surface means a bigger, more stable bacterial colony processing ammonia and nitrite into far less toxic nitrate.Good to Know: Because much of the colony lives inside the pores, Matrix is completely inert and essentially permanent — it doesn't exhaust or break down, so you never need to replace it, only give it the occasional rinse if it clogs with detritus. Seachem also notes that in slow-flow filters the deep pores can host anaerobic bacteria that consume nitrate, though that's a long-term, gradual effect rather than an overnight nitrate fix. It works in any filter: HOB, canister, or sump.Where It Goes: In any filter, water should pass through media in this order — first mechanical (sponge/floss to catch debris), then chemical (carbon and similar), then biological (bio-media). Putting mechanical media first keeps the others from clogging with gunk and makes them last far longer.How to Use: A rough guide is 1–2 liters of Matrix per 100 gallons. Place it after your mechanical and chemical media, in a media bag if your filter needs it. When maintaining, rinse it only in old tank water (never chlorinated tap water, which kills the bacteria), and stagger any media swaps so you never disturb the whole colony at once.