Alkalinity (Carbonate hardness) in Ponds
Understanding Alkalinity in Your Pond
Alkalinity, also known as carbonate hardness or German carbonate hardness (dKH), is a crucial factor in maintaining healthy pond water. It measures the concentration of carbonates and bicarbonates, which act as a buffer to neutralize acids and help stabilize pH levels.
While pH measures how acidic or basic water is, alkalinity reflects the water’s ability to resist changes in pH.
How Alkalinity Works
Alkalinity is measured in:
- Degrees of carbonate hardness (dKH)
- Parts per million (ppm) of calcium carbonate (CaCO₃)
- Milligrams per liter (mg/L)
Water with high alkalinity can still have a neutral or even low pH, and vice versa. Alkalinity is influenced by dissolved minerals like calcium and magnesium, which are more abundant in hard water.
Over time, bacterial processes in the pond produce acidic byproducts that reduce alkalinity, so regular monitoring is important.
Ideal Alkalinity Levels
- Target range: 100 ppm is ideal
- Acceptable range: 50–200 ppm
High alkalinity is usually kept in check through regular water changes, assuming the replacement water has a lower alkalinity than your pond.
When to Supplement
Ponds with EPDM liners, vinyl liners or fiberglass construction tend to lose alkalinity more quickly and may require supplementation. You can raise alkalinity by adding:
- Calcium carbonate
- Concrete blocks
- Oyster shells
- Limestone
- Crushed egg shells
Maintenance Tips
- Regularly remove sludge and decaying organic material from the pond and filtration system.
- Perform weekly water changes (10% for smaller ponds; less for large ones).
- Use test kits to monitor and maintain both pH and alkalinity.
Keeping your alkalinity stable helps ensure a healthy, thriving environment for koi and pond life.