pH
pH
What is it
pH measures how acidic or alkaline the water is. The scale is logarithmic, so a move from 7 to 6 is not small: it means ten times more acidity.
Why it matters
pH affects gill function, bacterial performance, nutrient availability and the toxicity balance between ammonium and ammonia. Most aquarium animals adapt to a range, but they do poorly with sudden shifts.
Interactions with other parameters
KH buffers pH, CO2 lowers pH while it is dissolved, and ammonia becomes more dangerous as pH rises. Always read pH together with KH and temperature.
Ideal ranges
| Tank type | Min | Max | Unit |
|---|---|---|---|
| Tropical community | 6.5 | 7.5 | pH |
| Planted high-tech | 6.0 | 6.8 | pH |
| Planted low-tech | 6.5 | 7.8 | pH |
| Shrimp tank | 6.0 | 7.0 | pH |
Out of range: what happens
Very low pH can slow nitrifying bacteria and stress hard-water species. Very high pH increases the share of toxic free ammonia and can block some plant nutrients. Rapid corrections may shock fish and shrimp.
Common Myths
- •Every fish needs an exact pH; stable water in a suitable range is usually safer.
- •pH-down products solve the cause; without changing KH, the value often rebounds.
How to measure
Use a liquid test kit or calibrated pH meter. Test at the same time of day when comparing readings, because CO2 and photosynthesis can move pH between morning and evening.
How to adjust
Change pH by changing the buffering system, not by chasing numbers with acids or bases. RO water, active soil, peat or botanicals can lower it; carbonate minerals and harder source water can raise and stabilize it.
Pro Tips
For CO2 tanks, compare pH before injection and during peak injection to estimate dissolved CO2.
Acclimate sensitive shrimp slowly when moving between different pH and KH values.
