Important water parameters and their desired values Parameter Importance pH value All creatures in aquariums react sensitively towards pH value changes. Depending on the species kept, the pH value should be in the slightly acidic or a neutral (7) to slightly alkaline (8) range. Sudden pH value changes (such as rapidly sinking pH value) are very dangerous. Desired value 6 – 8 Carbonate hardness (KH) The KH is defined by the hydrogen carbonate ion concentration in the water. Sufficiently high KH (at least 6°dKH) reliably buffers dangerous pH value variations. 6 – 10°dKH Ammonium/ Ammonia (NH4/NH3) Nitrite (NO2) Waste and breakdown product (of proteins), part of the nitrification cycle and a dangerous fish poison! Good biological activity provided, it is ideally not detectable. < 0.5 mg/l (better 0 mg/l) Waste and breakdown product (of proteins), part of the nitrification cycle and also a dangerous fish poison! Good biological activity provided, it is ideally not detectable. < 0.5 mg/l (better 0 mg/l) Total hardness (GH) The GH is formed by the entirety of alkaline earth ions (mainly calcium and magnesium) and serves as an important mineral source. 6 – 15°dGH Nitrate (NO3) Breakdown product and component of the nitrogen cycle. Hardly toxic plant nutrient that, however, supports algae growth in higher concentrations. < 50 mg/l Phosphate (PO4) Waste and breakdown product. Hardly toxic plant nutrient that, however – especially in higher concentrations –, is the most important support for uncontrolled algae growth. < 1 mg/l Copper (Cu) Heavy metal already toxic in low concentrations, but also essential trace element as well as effective agent in some treatments and biocides. < 0.1 mg/l Silicate (SiO3) Diatoms are characterized by their silicate containing cell walls. Silicate levels above 2 mg/l in the aquarium water support their growth. < 2 mg/l Oxygen level (O2) O2 is essential for all aquarium inhabitants for breathing, but it is also im- portant for breakdown processes (uneaten food, fish waste, plant parts etc.). It is normal that the saturation changes according to the time of day due to photo synthesis. Good water agitation and not too warm water support the supply. > 4 mg/l (better > 6 mg/l) Tip: Certain fi sh species (e.g. discus, angelfi sh or African cichlids) require water pa- rameters that differ from these general desired values, especially for breeding. Your retailer knows about the species specifi c data concerning the optimal water hardness, the suitable pH value and other conditions (e.g. oxygen requirement). 6