process
Chemical filtration
Useful as a targeted tool and unnecessary as a permanent fixture. Activated carbon is the most commonly used and the most commonly misunderstood: it removes dissolved organics and medication, becomes exhausted within weeks, and does nothing at all for ammonia, nitrite or nitrate.
In one sentence
Chemical filtration uses adsorbent or ion-exchange media to remove specific dissolved substances — tannins, medications, phosphate, organics.
When it earns its place
- Removing medication at the end of a treatment course.
- Clearing tannin staining from new wood, if you want the water clear.
- Removing a specific pollutant after an accident.
What it does not do
Carbon does not remove ammonia, nitrite or nitrate. Left in the filter indefinitely it stops adsorbing and simply becomes additional biological media, which is harmless but is not what it was bought for. Running carbon permanently also removes any medication you later add, which catches people out mid-treatment.