| Nitrite is just as toxic as ammonia. It affects the | | | | A planted watercourse will take up nitrate and |
| oxygen carrying capability of the blood. Because it | | | | phosphate which is another fertilizer from the |
| also irritates their skin, koi may jump out of the | | | | water and may help to reduce the amount of |
| water and flick or rub themselves on the pond | | | | filamentous algae present in the pond. Vegetable |
| bottom or walls. These are symptoms of high | | | | filters will require maintenance in autumn and |
| nitrite levels and if exposed to them for a | | | | spring and have a minimal, if any, effect during |
| prolonged period, koi will become listless and die. | | | | the winter months when the plants die back. |
| Keep nitrite to an acceptable level by carrying out | | | | If a planted water course is switched off in the |
| water changes to dilute it. Continue daily water | | | | colder months to minimize cooling, give it a |
| changes and testing until zero nitrite has been | | | | thorough clean before reintroducing it into the |
| reached. As with high ammonia levels, reduce | | | | system to prevent polluting the main pond. |
| feeding during this time to cur down the load on | | | | The test kit uses chemicals in tablet form to |
| developing filter biomass. | | | | measure the nitrite content of the water. Some |
| This is the end product of the nitrogen cycle. | | | | test kits use liquid chemicals to produce the color |
| Although it is less toxic than ammonia or nitrite, | | | | change. After an appropriate time has elapsed, |
| do not allow the nitrate level to exceed 100 mg/l | | | | compare the color of the water in the test tube |
| and aim for a reading of 50 mg/l or less. A | | | | to that on the chart to ascertain the level of |
| separate vegetable filter or a planted pond can | | | | nitrite in the water. |
| help to reduce nitrate levels. | | | | |