Key Aquarium Water Parameters
An overview of the core water parameters to monitor: temperature, pH, ammonia, nitrite, nitrate, GH and KH, with target ranges and testing.
Why parameters matter
Water chemistry determines whether fish and plants stay healthy. The most important parameters to monitor are temperature, pH, the nitrogen compounds (ammonia, nitrite, nitrate), and water hardness (GH and KH). Regular testing catches problems before they become visible in the fish.
Temperature
Temperature drives metabolism and oxygen solubility. It is set to suit the species kept and should remain stable. Temperature also influences chemistry: higher temperature increases the toxic un-ionised fraction of ammonia and the speed of biological processes.
pH
pH is the logarithmic measure of acidity; 7 is neutral, below 7 acidic, above 7 alkaline. Each unit represents a tenfold change in hydrogen ion concentration. Stability matters more than chasing a specific number, and pH stability depends on carbonate hardness (KH).
Ammonia and nitrite
Ammonia and nitrite are produced by waste and are toxic. In a cycled tank both should read effectively zero. Even low ammonia can damage tissues; tissue damage in fish can occur around 0.05 mg/L of un-ionised ammonia, and nitrite is also toxic at low concentrations.
Nitrate
Nitrate is the comparatively non-toxic end product of nitrification. It is controlled by water changes and plant uptake. Many keepers maintain nitrate roughly in the 40-80 ppm range, aiming lower mainly to limit algae.
GH and KH
General hardness (GH) reflects dissolved calcium and magnesium; carbonate hardness (KH, or alkalinity) reflects carbonate and bicarbonate and buffers pH. Soft-water species and many plants do best at low KH, while hard-water species prefer higher mineral content.
Testing
Liquid reagent test kits or calibrated meters are used to measure these parameters. New and recently changed tanks should be tested frequently; established tanks can be tested on a routine schedule plus whenever fish show distress.