The goal for your pond should not be a “clean” and “clear” pond. If it is too sterile it is not good for the fish. I’m not saying it should be so murky that the fish can’t be seen. I’m only saying that it should not be shiny clean like the floors and windows of your house. Normally the correct filtration system will keep your pond levels where they should be if you occasionally make water changes, you feed the fish properly by not giving them too much food, and if you do not have more fish than your pond should hold.
Ammonia levels are directly related to the amount of food, fish waste, and decaying matter in the pond. This can become toxic to your fish. Pay attention to your fish and they will tell you there is a problem. If levels of ammonia are too high it will cause the fish to look like they are bleeding and cause excess mucus. The fish will become lethargic, quit eating and could develop flashing.
Nitrite is formed when bacteria process the ammonia. Nitrite is known as the invisible killer. Nitrites can’t be seen but can cause damage to the liver, spleen, kidneys and nervous system of your Koi. Your fish usually will show the problem through their gills. The gills do not lay flat against the Koi’s body and the gills look like they are rolled out at the edge. Fish that are exposed to low levels of nitrite for a long time will suffer damage to their immune system. If untreated the fish die from a secondary disease or a lack of oxygen.
Nitrates are not as toxic as nitrites. They are produced by bacteria combining oxygen and nitrite. This can be the silent killer because it usually isn’t monitored by the average pond owner. When levels are too high it will cause an ulcer disease and death.
Monitoring of the steps in the nitrogen cycle is very important to the health of your Koi. Acceptable levels are listed next.
• Ammonia’s ideal reading would be zero. Koi can tolerate an ammonia level of 1 ppm (parts per million) at a temperature of 70 degrees for a day or two if the pH level is 7-10. Higher levels are dangerous.
• A pH level is the measure of Hydrogen ions in the water. A normal reading is 7-8.5. Acceptable could be in the range of 6-9. Readings over 9 can cause kidney disease if left untreated.
• Nitrite levels should be zero. Readings can increase when adding a lot of fish or when temperatures rise. Fish activity may increase faster than the bacteria activity.
• Nitrate levels will be 50-100 ppm. The acceptable range is up to 200 ppm but below 100 is best.
I can’t say it enough times; you control the levels in your pond. There are 3 main things that you will need to do to prevent problems. First you need to make sure you don’t have too many fish in your pond. Too many fish will create too much waste for the filter system than planned. The second thing is to make sure you have purchased a filter large enough for your pond. Third, do not over feed your Koi and remove any food they do not eat. Also remove any debris sitting at the bottom of your pond.