dKH
KH
What is it
KH, or carbonate hardness, measures the water buffering capacity. It tells you how strongly the aquarium resists pH change.
Why it matters
A stable buffer protects livestock and bacteria from sudden pH drops. At the same time, very high KH makes it difficult to keep soft acidic water or some active-soil shrimp systems.
Interactions with other parameters
KH, pH and CO2 are tightly linked. Injected CO2 lowers pH temporarily, but KH decides how much the pH moves.
Ideal ranges
| Tank type | Min | Max | Unit |
|---|---|---|---|
| Tropical community | 3 | 10 | dKH |
| Planted high-tech | 2 | 5 | dKH |
| Planted low-tech | 3 | 12 | dKH |
| Shrimp tank | 0 | 2 | dKH |
Out of range: what happens
Low KH can allow pH crashes, especially in stocked tanks with acids from nitrification and organics. High KH can keep pH high and fight against CO2 or soft-water setups.
Common Myths
- •KH and GH are the same; they measure different parts of water chemistry.
- •Zero KH is always ideal for plants; it can be risky in community tanks without active management.
How to measure
Use a liquid KH titration kit and count drops to the color change. Test after large water changes and when using active soil, carbonate rocks or RO water.
How to adjust
Raise KH with bicarbonate or carbonate-based buffers in small measured doses. Lower KH by diluting with RO water, active substrate or careful acidifying methods that do not create sudden swings.
Pro Tips
Keep KH changes gradual: one or two degrees per maintenance cycle is safer for most tanks.
If pH moves wildly between day and night, check KH before blaming CO2 alone.
