Filters confuse people because they look dirty when they’re doing their job. In a guppy tank, the filter is the heart of stability. It’s where beneficial bacteria live and process waste. When people replace filter media to make it look “fresh,” they often remove the bacteria colony — and the tank behaves like it’s brand new again. That’s why “new media” is a common cause of sudden ammonia issues.
The biggest filter myth
Myth: You should replace filter media regularly.
Reality: You should replace media only when it is physically falling apart. Most media should be rinsed, not replaced.
What to clean
- Intake and impeller area: remove slime that reduces flow.
- Mechanical sponges: rinse in old tank water when flow drops.
What to leave alone
- Biological media: keep it wet and don’t scrub it clean.
- “Dirty” brown biofilm: it’s often the working bacteria colony.
How to clean safely
- take a bucket of old tank water during a water change
- swish sponges gently (don’t wring them to death)
- reassemble quickly so media doesn’t dry out
A filter doesn’t need to look pretty. It needs to move water and host bacteria. If you respect that, guppy tanks become much more stable and far less prone to “mystery problems.”
