Ammonia

What it is

Ammonia is what comes out of a fish continuously, plus whatever leaves uneaten food and decaying plant matter. In water it exists in two forms that trade back and forth: ammonium, which is charged and comparatively mild, and free ammonia, which is uncharged and burns gill tissue. A hobby test kit does not separate them. It reports the two added together and calls the total ammonia. That single number is therefore not a toxicity reading on its own — it is a quantity, and how much of that quantity is in the dangerous form depends on the water it is sitting in.

Why it matters

The split between the two forms moves with pH and with temperature. Warmer water and higher pH push more of the total into the free ammonia form; cooler and more acidic water push it back toward ammonium. This is why the same 1 ppm reading is a different situation at pH 6.8 and 74 °F than it is at pH 8.2 and 82 °F, and it is why EPA writes its aquatic life criterion for ammonia as a function of pH and temperature rather than as a single number. In a tank, ammonia is also a timer: it is the first thing that appears when the biological filter is missing, overloaded, or has been damaged, so a reading above zero is usually telling you something about the filter rather than about the fish.

What each band means

How to test it

1. Test before a water change, not after. A reading taken twenty minutes after you swapped half the water tells you about the tap, not about the tank.
2. Draw the sample from mid-water, away from the filter outflow and away from the substrate. Both of those places read unrepresentatively.
3. With a liquid kit, hold the reagent bottles vertical and count drops slowly. A partial drop is the single most common source of a wrong ammonia number.
4. Read the tube against the white part of the card in daylight, not against a lamp and not against the tank. Colored light shifts a yellow-to-green scale badly.
5. Wait the full time printed on the instructions before reading. The ammonia test is one of the slower ones and an early read runs low.

How to move it

1. Change water. This is the only step that removes ammonia rather than converting or masking it, and it works immediately at whatever percentage you swap.
2. Stop feeding for a day or two. Fish are fine; the waste stream is what you are trying to shrink.
3. Find what died. A lost fish behind the filter or under a rock will hold a reading up on its own no matter how much water you change.
4. Check that the filter is running and that its media was not recently replaced wholesale or rinsed under the tap. Both of those remove the bacteria that were handling the ammonia.
5. Only then consider a bottled bacteria product, and read it as a way of shortening a cycle rather than as a fix for a maintenance problem.

Where the reading goes wrong

• Testing tap water and finding ammonia, then assuming the kit is broken. Chloramine-treated tap water contains ammonia by design, and several conditioners split chloramine into chlorine and ammonium, which the kit then reads.
• Using a conditioner that binds ammonia and expecting the reading to drop. Most of those products convert ammonia to a less harmful form; the total ammonia test still counts it.
• Shaking bottle 2 too briefly. The second reagent in a salicylate kit settles and needs a genuine shake, not a swirl.
• Comparing tubes side by side that were filled at different times, then reading the older one as the current state of the tank.

Problems that start here

• Act today

  My new tank is reading ammonia and there are already fish in it

• Act this week

  The water has gone cloudy and white

• Act this week

  All four readings are fine but the tank smells bad

• Act this week

  My test strips and my liquid kit give different answers