Concentration and Mass Fractions

• mg/L (milligrams per liter) - primary unit of nutrient concentration in aquarium water
• ppm (parts per million) - parts per million, equivalent to mg/L for aqueous solutions
• % (percent) - percentage content of element in fertilizer or reagent
• g/L (grams per liter) - concentration for highly concentrated solutions

Water Hardness

• °dGH (degrees of German hardness) - unit of general hardness (GH), 1°dGH = 17.8 mg/L CaCO3
• °dKH (degrees of carbonate hardness) - unit of temporary hardness (KH), 1°dKH = 17.8 mg/L CaCO3

Acidity and Alkalinity

• pH (hydrogen ion concentration) - logarithmic acidity scale from 0 to 14
• pH units - dimensionless quantity

Volume and Flow

• L (liter) - primary unit of aquarium volume and water changes
• mL (milliliter) - unit for fertilizer and reagent dosing
• L/h (liters per hour) - filtration rate

Reagent Mass

• g (gram) - primary unit of mass for weighing reagents
• mg (milligram) - precise microelement dosing

Lighting

• μmol/m²/s (micromoles per square meter per second) - unit of PAR measurement
• lumen (lm) - luminous flux of light source
• lux (lx) - surface illuminance
• Kelvin (K) - color temperature of light

Gases

• mg/L - concentration of dissolved CO2 in water
• bubbles per second - CO2 supply rate through bubble counter
• bar - pressure in CO2 supply system

Time

• hours (h) - photoperiod duration
• days - frequency of water changes and fertilizer dosing
• weeks - cycles in fertilizer dosing schedule

Solubility

• g/100mL - standard solubility unit at specific temperature
• g/100g H2O - solubility in grams of water

Temperature

• °C (degrees Celsius) - water temperature and reagent solubility conditions

Electrical Conductivity

• μS/cm (microsiemens per centimeter) - water electrical conductivity
• mS/cm (millisiemens per centimeter) - for highly mineralized water