The short answer
If your tap water tests positive for ammonia, it’s almost always because your supply is treated with chloramine — chlorine bonded to ammonia. The fix is a water conditioner that detoxifies ammonia and chloramine, not just chlorine. A conditioner like Prime neutralises chlorine, breaks down chloramine and detoxifies the ammonia it releases, all in one dose — added every time you use tap water.
Why the ammonia is there
To keep mains water safe, many utilities use chloramine instead of plain chlorine because it’s more stable in the pipes. The catch for aquarists: chloramine is chlorine plus ammonia. A basic dechlorinator that only tackles chlorine leaves the ammonia behind — which is why your tap water can read as containing ammonia even before it reaches the tank.
The right kind of conditioner
- Choose one that names ammonia and chloramine, not just “removes chlorine.” These products bind chlorine, split the chloramine bond, and convert the freed ammonia into a form that’s non-toxic and that your filter bacteria can still process.
- Dose for the volume you’re adding, every water change and every top-up with tap water.
- It works instantly, so the water is safe to add straight after dosing.
Next steps
Check your source first with a water test kit so you know whether ammonia is present, then dose a conditioner that handles it — see our conditioner picks. For the tap-water basics see is tap water safe for aquarium fish? and can I use tap water for a water change?. If ammonia shows up inside the tank rather than the tap, see how to lower ammonia fast and browse water testing.