What is pH in aquariums?
pH is a logarithmic scale that measures how acidic or alkaline aquarium water is.
- pH 7.0 is neutral
- Below 7.0 is acidic
- Above 7.0 is alkaline (basic)
Each whole pH unit represents a 10× change in acidity or alkalinity.
Why pH is important for fish
Fish species evolved in specific water conditions. Incorrect or unstable pH can lead to:
- Chronic stress
- Weakened immune systems
- Poor growth and coloration
- Breeding problems
- Increased disease risk
Sudden pH changes are often more harmful than a slightly incorrect but stable value.
Common pH ranges by aquarium type
- Amazonian / blackwater fish: 5.0–6.5
- General community tanks: 6.5–7.5
- African cichlids (Rift Lakes): 7.8–8.6
- Goldfish: 7.0–8.0
- Marine aquariums: 8.0–8.4
What affects pH in an aquarium
- Source water and treatment method
- Substrate, rocks, and driftwood
- Fish waste and uneaten food
- Biological filtration (nitrification lowers pH over time)
- CO₂ injection in planted aquariums
How to measure pH
- Liquid test kits (most reliable for hobbyists)
- Test strips (fast but less precise)
- Digital pH meters (accurate with proper calibration)
Managing pH safely
- Match pH to the fish species, not the other way around
- Make adjustments gradually
- Prioritize long-term stability
- Use natural methods (driftwood, crushed coral) before chemicals
pH should always be evaluated together with KH (carbonate hardness) and GH (general hardness), as they influence buffering capacity and stability.