Aquarium calculators
Free calculators for everyday fishkeeping: species compatibility, tank volume, water changes and nitrates, CO₂, water hardness and salinity.
- What fish can I keep? Species for your tankFind fish, shrimp, corals and plants that suit your tank by volume, temperature, pH and difficulty.
- Fish and species compatibility checkerCheck whether several fish, shrimp, corals or plants can live together: water type, temperature, pH, tank size, temperament and group size.
- Aquarium volume calculatorWork out your tank’s real water volume from its dimensions, minus the substrate and the gap below the rim.
- Water change and nitrate calculatorHow much water to change and how far each change will lower your nitrates.
- CO₂ calculator from KH and pHWork out dissolved CO₂ in a planted tank from KH and pH.
- Water hardness converter (GH and KH)Convert water hardness between German degrees (°dH), ppm CaCO₃, mmol/l and mEq/l.
- Salinity and sea salt calculatorConvert specific gravity and salinity (ppt) and work out how much salt you need to mix saltwater.