Water parameters: what to measure and why
A small planted freshwater aquarium. Source: Wikimedia Commons.
Water chemistry is the part of fishkeeping that beginners most often skip and later regret. You cannot see ammonia, and a tank can look clear while the water harms its inhabitants. The goal is not to hit a single perfect number but to keep conditions stable within a range the chosen species tolerate.
The parameters that matter
| Parameter | What it describes | Practical note |
|---|---|---|
| Temperature | Warmth of the water | Most community tropicals sit in a warm range; abrupt changes stress fish more than the exact value. |
| pH | Acidity or alkalinity | Stability matters more than a target; many common species adapt to a steady local pH. |
| Ammonia (NH3) | First waste product | Toxic. Should read zero in an established tank. |
| Nitrite (NO2) | Second cycle stage | Toxic. Should read zero in an established tank. |
| Nitrate (NO3) | Final cycle stage | Low toxicity; controlled by water changes and plants. |
| Hardness (GH/KH) | Dissolved minerals | Influences which species and plants thrive, and how stable pH stays. |
The nitrogen cycle in plain terms
Fish produce waste, and uneaten food decays. Both release ammonia. In a healthy tank, one group of bacteria converts ammonia into nitrite, and a second group converts nitrite into nitrate. Ammonia and nitrite are toxic; nitrate is comparatively safe and is removed by routine water changes.
A tank is "cycled" once it processes ammonia all the way to nitrate quickly enough that ammonia and nitrite both read zero. Until then, it is not ready for a full load of fish.
For a clear technical overview of the underlying biology, the Wikipedia entry on the nitrogen cycle is a reasonable starting reference.
Canadian tap water notes
Two local details affect Canadian keepers in particular:
- Many municipal systems treat water with chloramine rather than plain chlorine. Chloramine does not dissipate by letting water sit out, so a conditioner that neutralizes chloramine is usually needed before water enters the tank.
- In winter, cold tap water can be far below tank temperature. Adding large volumes of very cold water during a change can shock fish, so matching temperature before a change is worth the extra minute.
For region-specific guidance on water treatment, your municipal water provider publishes annual water-quality reports that state whether chlorine or chloramine is used.
- Test ammonia, nitrite, and nitrate during the first weeks of a new tank.
- Change a portion of the water on a regular schedule to keep nitrate low.
- Treat replacement water for chlorine/chloramine and match temperature.
- Feed conservatively — excess food is a common ammonia source.