The short answer
It depends on the media type — but the golden rule is never replace it all at once. Sponges and bio media can last years; only fine floss and chemical media (carbon) are true consumables that need regular swapping. Whatever you change, keep most of your colonised media in place so your beneficial bacteria — and your cycle — survive.
By media type
- Coarse & fine sponge: rinse in old tank water every few weeks; replace only when they fall apart, often after a year or more.
- Filter floss / polishing pad: the most disposable layer — replace every 2–4 weeks as it clogs.
- Ceramic rings / bio media: last for years. Rinse occasionally; replace a portion only if crumbling.
- Activated carbon / chemical media: exhausts in 3–4 weeks, then it’s just inert surface area. Replace monthly if you use it at all.
Why “all at once” is a trap
Your biological filtration lives on the media surface. Replace everything in one go and you bin the bacteria that convert ammonia to nitrate, causing a dangerous spike. This is the single most common way keepers accidentally crash a healthy tank.
The safe routine
Stagger it: rinse sponges on one maintenance day, swap floss on another, and never touch bio media and mechanical media in the same session. For the full method see how to clean an aquarium filter and how often should I clean my aquarium filter. To understand what each layer does, read what is aquarium filter media, or browse the aquarium filters hub.