Water parameters

This is a table of values/substances that may be relevant to measure in the aquarium.
Water parameter	Measurement unit	Area	Note
Temperature	°C, °F	25 - 28 °C	Temperature is the most important and easiest water value to measure. Bettas can withstand down to 20 °C and up to 34 °C, but such extreme temperatures become a burden on their immune system. Bettas also do not like the temperature in the aquarium to fluctuate too quickly.
Hardness	°GH, °KH, °dH	0 - 25 °GH	Hardness says something about how much dissolved salts the aquarium water contains. This affects the fluid/salt balance of the fish. High hardness also makes the pH value in the water more stable.
Acidity	pH	6 - 8	Acidity (pH value or simply pH) is an important water value. Neutral aquarium water has a pH of 7.0. Bases (alkaline substances) have a higher pH, up to 14. Acids have a lower pH, down to zero. Acidity is related to hardness: As the hardness increases, the minimum pH usually follows. That means hard water (high GH) usually has a more stable pH than softer water. The pH value should be measured at a fixed time of day because the plants' increased CO₂ production during the day causes the pH in the aquarium to drop.
Ammonia (NH₃) (English: ammonia)	ppm, mg/l	< 0.25 mg/l in total	Ammonia is excreted by the fish, both in urine and directly from the gills. This substance is highly toxic. Ammonia and ammonium are preferably measured together. Their mutual relationship depends on the pH value. High pH gives more ammonia and less ammonium. Ammonia is the more toxic of the two, so if the pH is high, it is even more important to avoid NH₃/NH₄₊ in the water. These substances are normally only found in measurable quantities in newly set up or overfed aquariums. They can also occur as a result of dead and rotting fish or a failing aquarium filter. Bacteria in the filter break these substances down to nitrite, which is less toxic.
Ammonium (NH₄₊) (English: ammonium ion)	ppm, mg/l	see above	see above
Nitrite (NO₂₋) (English: nitrite)	ppm, mg/l	< 0.8 mg/l	Nitrite in larger quantities is usually only found in new or overfed aquariums. In a stable aquarium, nitrite should hardly be measurable. Bacteria in the filter break down nitrite into nitrate, which is less toxic.
Nitrate (NO₃₋) (English: nitrate)	ppm, mg/l	< 25 mg/l	Nitrate is not further broken down to any significant extent. The only effective way to get rid of it is to change the water. Although nitrate is less toxic than nitrite and ammonia, high concentrations can be harmful to fish. Too much nitrate can also cause algae problems in the aquarium.