Why Water Quality Comes First
The vast majority of koi health problems trace back to water quality. Test regularly with a liquid master kit and you'll catch issues before they become emergencies.
The Four Key Parameters
- pH — aim for a stable 7.0–8.5. Sudden swings stress koi more than the absolute value.
- Ammonia (NH3) — target 0 ppm. Highly toxic; produced by fish waste and uneaten food.
- Nitrite (NO2) — target 0 ppm. Also toxic; an intermediate in the nitrogen cycle.
- Nitrate (NO3) — keep low (under ~40 ppm) via water changes and plants.
The Nitrogen Cycle
Beneficial bacteria in your filter convert toxic ammonia → nitrite → far less harmful nitrate. A new pond must 'cycle' before it can safely hold many fish — dosing beneficial bacteria speeds this along.
Good Habits
- Test weekly, and always after adding fish or treatments.
- Perform regular partial water changes, treating new water with a conditioner.
- Don't overfeed — excess food is the most common cause of water-quality crashes.