ppm total ammonia nitrogen
Ammonia
Total ammonia — the ammonium ion plus free ammonia, added together.
4 bands · 5 testing steps
Reference
The Six Numbers That Decide Everything
Almost every troubleshooting page on this site starts by asking you to test something. These are the things it asks for: what each one measures, what the bands mean, and which testing mistakes produce a number you should not have trusted.
Two of these — ammonia and nitrite — are acute. A bad reading means act today. Two of them, nitrate and pH, are chronic: they tell you about your habits over weeks rather than about this afternoon. Temperature sits underneath all of it, because it changes the rate at which everything else happens. And chlorine is the one that arrives from outside the tank entirely.
Where a published standard exists, the bands on these pages cite it. Where the right value depends on the species you keep, that is said plainly instead of being averaged into a figure that suits nobody.
ppm nitrite
Nitrite
Nitrite ion, the intermediate product between ammonia and nitrate.
4 bands · 4 testing steps
ppm nitrate ion
Nitrate
The nitrate ion — note that drinking water standards are written as nitrate-nitrogen, which is a different number.
4 bands · 5 testing steps
pH units, with KH in dKH
pH and KH
Acidity of the water, plus the carbonate buffer that resists changing it.
4 bands · 4 testing steps
°F, with °C alongside
Temperature
The temperature of the water itself — not of the room the tank sits in.
4 bands · 5 testing steps
ppm as Cl₂
Chlorine and Chloramine
Residual disinfectant carried in from the tap.
3 bands · 4 testing steps
Which to test, and when
| Situation | Test this | Why |
|---|---|---|
| Tank under eight weeks old | Ammonia and nitrite, daily | These two place you on the cycle. Nothing else matters until they hold at zero. |
| Established tank, routine check | All four, weekly | The value is the record over time, not any single reading. |
| Algae or a nutrient problem | Nitrate, before the water change | The pre-change number is the peak, and the peak is what your interval has to handle. |
| pH looks unstable | pH and KH together, same session | A pH reading without a KH reading cannot be interpreted at all. |
| New tap supply, or a utility notice | Chlorine, plus nitrate and KH from the tap | What arrives at your house sets the floor and the ceiling for what a water change can do. |
| Fish at the surface on a warm day | Temperature, at both ends of the day | Warm water holds less oxygen, and the daily swing is usually the real problem. |