The short answer is: almost never. A mature filter is a living ecosystem; swapping it out wipes out the beneficial bacteria that keep your fish alive. Instead, focus on keeping that colony healthy and only replace the parts that actually wear out.
Mechanical media (sponges, pads, floss)
Rinse these in a bucket of tank water every two to four weeks, or whenever water slows. When fibers start to fall apart—usually after six to twelve months—swap one pad at a time so you don’t crash the cycle. If your filter has multiple sponges, stagger their replacements by a month.
Biological media (ceramic rings, sintered glass, bio-balls)
These never need to be replaced unless they crumble in your hand. Once a year, give them a gentle swish in old tank water to remove loose sludge, then put them right back.
Chemical media (carbon, resins, phosphate removers)
These do get exhausted, so follow the manufacturer’s timeline—typically three to six weeks. When you toss them, cut the new pouch to size and slide it into the same compartment to keep flow patterns unchanged.
Signs something is off
- Water flow drops even after rinsing mechanical media.
- Ammonia or nitrite creeps above zero.
- The filter body cracks or the impeller starts grinding.
In those cases, replace the failing part (impeller, housing, or whole unit) but keep as much old media as possible. Stuff the seasoned rings or sponge into the new filter and run both together for two to three weeks. Your bacteria colony will thank you, and so will your fish.
Post time: Aug-14-2025