Why it matters
Ammonia burns gills and damages organs. In a cycled tank it should always read zero. Any detectable ammonia is an emergency.
Ideal ranges
| Water type | Ideal | Acceptable |
|---|---|---|
| Freshwater aquarium | 0.0 | below 0.25 short-term |
| Saltwater / reef | 0.0 | below 0.1 short-term |
| Pool / spa | 0.0 | — |
| Koi pond | 0.0 | below 0.25 short-term |
- Pool / spa: Ammonia in pools indicates contamination or chloramine breakdown.
How to test
- 1
Use a liquid test kit
Strips for ammonia are notoriously unreliable. API, Salifert, and Red Sea drop kits are accurate.
- 2
Test at the same time daily during a cycle
Morning readings before feeding give the truest baseline.
- 3
Read against a white background in natural light
Yellow-green hues are subtle. Daylight reveals shifts strips would miss.
How to correct high ammonia
Stop feeding immediately
No food in for 24 to 72 hours while ammonia is detectable. Fish can safely fast that long.
Perform a 25 to 50 percent water change
Use temperature-matched, dechlorinated water. Repeat daily until ammonia reads zero.
Add a detoxifier
Seachem Prime binds ammonia for 48 hours so the biofilter can catch up. Dose for the full tank volume.
Verify the biofilter is alive
Recent filter media swap, antibiotic dose, or power loss can crash the cycle. Add bottled bacteria if needed.
Common causes
- •Uncycled or recently cycled tank
- •Filter media replaced all at once
- •Overstocking or overfeeding
- •Dead fish or hidden uneaten food
- •Chloramine breakdown in pools
FAQs
Why is my ammonia high after a water change?
Tap water with chloramine releases ammonia when dechlorinator breaks the chlorine-ammonia bond. Use Prime or a dechlorinator that detoxifies ammonia.
Can plants remove ammonia?
Yes. Fast-growing plants like hornwort, water sprite, and pothos directly absorb ammonia. They can buffer a small spike but not replace a cycled biofilter.