Guide · Water changes and testing
Free vs total ammonia
A badge that reads free ammonia and a kit that reads total ammonia can both be right. Why the numbers differ so much, and how to use each test without panic.
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Short answer
Ammonia in tank water exists in two forms. Free ammonia is the un-ionized part; total ammonia counts both forms together. A reading of one cannot be compared with a reading of the other: Seachem gives the example that 0.02 mg/L free ammonia equals 3.6 mg/L total ammonia in freshwater at pH 7.0. Check which form each test reports before you compare them.
Two forms, one problem
In water, ammonia is split between the free, un-ionized form and the ionized form. A test that reports total ammonia adds both. A test that reports free ammonia reads only the first, so its number is smaller. How the split falls depends on the water's pH and temperature, which is why the same total can mean a different free figure in a different tank.
Seachem's own example shows the size of the gap: 0.02 mg/L free ammonia equals 3.6 mg/L total ammonia in freshwater at pH 7.0.[1] At that pH, the total figure is 180 times the free one.
What each test reads
| Test | What it reports | How it works |
|---|---|---|
| Seachem Ammonia Alert | Free (un-ionized) ammonia[1] | A badge that stays in the tank and changes color; about 15 minutes to respond to a rise and about 4 hours to a fall[1] |
| API Freshwater Master Test Kit | Ammonia, plus pH, high-range pH, nitrite and nitrate, with seven test solutions[2] | Liquid tests you run by hand |
API's page, as we read it, does not say whether its ammonia result is free or total. Check the color chart and instructions in your kit to see which it reports before you compare it with a badge.
Reading Seachem's thresholds
Seachem gives Ammonia Alert color thresholds of about:[1]
| Seachem level | Free ammonia |
|---|---|
| ALERT | About 0.05 mg/L |
| ALARM | About 0.2 mg/L |
| TOXIC | About 0.5 mg/L |
These are free-ammonia figures. Do not hold a total-ammonia kit reading up against them; at pH 7.0, even a small free figure corresponds to a much larger total.
Using both
- The badge is a tripwire. A continuous monitor sits in the tank and shows a rise without you running a test, which helps between water changes and while you are away. Seachem says it lasts over a year but is not recommended in acidic water.[1]
- The kit is the full check. An aquarium test kit measures more than ammonia: API's covers pH, ammonia, nitrite and nitrate.[2]
- When the two disagree, first check which form each reports, then retest. If either shows ammonia rising, test again and do a water change.
Seachem's online-dealer list names specialist and pet retailers but not Amazon.[3] That does not mean an Amazon offer is fake; it is why the seller check matters.
Next
Questions
Why does my test kit show ammonia when my Seachem badge shows safe?
They may be measuring different things. Seachem says Ammonia Alert detects free ammonia, and gives the example that 0.02 mg/L free ammonia equals 3.6 mg/L total ammonia in freshwater at pH 7.0. A total-ammonia reading is a much bigger number for the same water.[1]
Which is more dangerous, free or total ammonia?
Free (un-ionized) ammonia is the form Seachem's thresholds are built on, with ALERT at about 0.05 mg/L, ALARM at about 0.2 mg/L and TOXIC at about 0.5 mg/L. Any rising ammonia reading in a tank is worth acting on.[1]
Does a continuous ammonia monitor replace a test kit?
No. Seachem's Ammonia Alert reads free ammonia only, and Seachem does not recommend it in acidic water. A kit such as API's Freshwater Master Test Kit also measures pH, nitrite and nitrate.[1][2]
How fast does Seachem Ammonia Alert react?
Seachem says it responds in about 15 minutes to rising ammonia and about 4 hours to falling ammonia, and that it lasts over a year.[1]