Testing water parameters correctly: what, when and how often?

Clear water is not necessarily good water. Many problems in the aquarium develop invisibly – long before fish fall ill or algae appear. If you know your water parameters, you can spot problems early and take targeted action.

But which parameters really matter? How often should you test? And which test method is worthwhile? This article gives you a practical overview for your freshwater aquarium.

The most important water parameters at a glance

Not every value needs to be measured constantly. For most community tanks, a few parameters are enough to reliably assess the condition of the water.

Nitrite (NO2) – the most important warning value

Nitrite is produced when leftover food and waste break down and is toxic to fish even in small amounts. In a well-established aquarium, bacteria quickly convert nitrite into nitrate. Ideally, nitrite should therefore be undetectable. If a value can be measured, action is needed: feed less and carry out a partial water change.

Nitrate (NO3) – the long-term indicator

Nitrate is the end product of the nitrogen cycle. It is much less toxic than nitrite but accumulates over time. Values below 25 mg/l are considered good for most aquariums. If nitrate rises sharply over time, this indicates infrequent water changes, too much food or overstocking. At the same time, nitrate is an important plant nutrient – without any nitrate, plant growth stalls.

pH value – acidic or alkaline?

The pH value indicates whether the water is acidic (below 7), neutral (7) or alkaline (above 7). Most common ornamental fish feel comfortable between 6.5 and 7.5. More important than a specific target value, however, is stability: strong fluctuations stress the animals more than a slightly different but constant value.

Carbonate hardness (KH) – the buffer

Carbonate hardness stabilises the pH value. If it is too low, the pH can drop quickly – a so-called acid crash. For most community tanks, a KH of around 4 to 10 °dH is a good range.

General hardness (GH) – the mineral content

General hardness mainly describes the content of calcium and magnesium. It is decisive for the choice of fish species: tetras and dwarf cichlids from soft-water regions prefer a low GH, while livebearers such as guppies or platies cope well with hard water. In many regions of Switzerland, tap water tends to be hard – it is worth choosing your fish accordingly.

Ammonium/ammonia (NH4/NH3)

Ammonium is also produced by the breakdown of organic matter. At high pH values, it is partly converted into ammonia, which is highly toxic to fish. In established tanks, ammonium is hardly detectable. A test is particularly useful during the cycling phase, after fish deaths or when the tank is overstocked.

How often should you test?

• During the cycling phase (first 4 to 6 weeks): test nitrite every two to three days. This lets you detect the so-called nitrite spike and know when the tank is ready for fish.
• In an established aquarium: test nitrite, nitrate, pH and KH approximately every two to four weeks. GH usually changes little and needs to be checked less often.
• When something seems wrong: test immediately if fish gasp for air, appear listless, algae suddenly appear or animals die.
• After changes: new fish, new food, filter cleaning or medication are good reasons for an additional check.

Test strips or drop tests?

Test strips provide an overview of several values at once within seconds. They are ideal for quick routine checks but are less accurate.

Drop tests take a little more effort but deliver more precise results. They are particularly recommended when problems arise, during the cycling phase and for sensitive fish species or shrimp.

A proven combination: test strips for regular checks, drop tests for precise analysis when something looks unusual.

Tips for reliable results

• Test before a water change – afterwards the values are distorted.
• Check the expiry date of the reagents and store them in a cool, dark place.
• Rinse test vials thoroughly with clean water after each test.
• Read colour values in daylight against a white background.
• Write down your results. This allows you to spot changes early before they become a problem.

Measure rather than guess

Regular water tests are among the simplest and most effective measures for a healthy aquarium. They replace gut feeling with clear facts and help you solve problems before your fish suffer.

At AQUATANA we offer a selection of proven test strips and precise drop tests for all important water parameters. We are also happy to advise you on which tests make sense for your aquarium and your stocking. Visit our online shop and keep an eye on the water quality of your aquarium at all times.