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Your First Pond

Koi pond

Published - 20061213, Revised:

Ponds are an enjoyable and relaxing garden feature. If you are like most new pond hobbyists, you can't wait to stock your pond with lots of fish. Before you run out and buy a bunch of fish for your pond, there are a few things you need to know about the new water world you created in your backyard that will help you save money, keep your new fish alive, and prevent disappointment. This article will address some common mistakes first-time pond owners make and explain a little about the water chemistry and biological processes that keep your pond healthy.

Nitrogen Cycle

When you first fill your pond with water, it is nearly a sterile environment. Ammonia which is toxic is excreted by fish through the gills. Aquatic systems need bacteria to process toxic chemicals into non-toxic chemicals.

Aerobic bacteria known as Nitrosospira and Nitrospira help break down ammonia (NH3) from fish and decomposing organic material (leaf litter) in a pond. These bacteria process ammonia into nitrite (NO2), and then into nitrate (NO3). Nitrite is also toxic, and nitrate has adverse health effects as it rises.

Plants and algae can take up nitrate as a fertilizer, thus completing the "Nitrogen Cycle."

Establishing Beneficial Bacteria

For the nitrogen cycle to complete, you must have enough Nitrosospira and Nitrospira bacteria to complete the process and maintain the ammonia and nitrite levels at 0 parts per million (ppm). Newly set up ponds do not have enough of these bacteria to keep the pond water safe for fish. Nitrosospira and Nitrospira are found in the environment but at very low levels. When water and ammonia are added to the pond, these bacteria will eventually heavily colonize the pond to the point that they can convert all the ammonia and nitrite to nitrate as fast as it gets created. In the beginning of establishing this bacteria in a pond, ammonia and nitrite levels can reach fatal levels for fish.

You can help the establishment of Nitrosospira and Nitrospira by adding gravel, sand, or rocks from an established aquarium or pond. Nitrosospira and Nitrospira live on the surface area of objects within a pond or aquarium. When introducing these objects, you seed the new system with these beneficial bacteria. If you do not have another established aquarium of pond, you can buy a bacteria in a bottle product that can help seed the system.

Even though you seed your new pond with good bacteria, you should wait to fully stock your pond. Add a few small fish to the pond, and give the bacteria at least 35 to 40 days at 75° to 80° F (23° to 26° C) to get well established in the pond, before you add more fish. How fast the bacteria will get established in the pond will depend on the water temperature. If the water is cooler than 75° F (23° C) it can take much longer for the bacteria to establish.

Water Tests

It is highly recommended that you purchase either a Freshwater or Pond Master Test Kit that has a pH, Ammonia, Nitrite, and Nitrate test kit. For your first month you will need to closely monitor the ammonia and nitrite concentration.

The first week after you add your first fish, you should check the ammonia and nitrite levels every two or three days. If the ammonia or nitrite levels reach 1 ppm, you should do a massive water change (90%) to reduce the concentration. Make sure the new water you add is de-chlorinated. Check the ammonia and nitrite a few days later to ensure the levels have not gone up again. It is essential to keep the ammonia and nitrite levels as low as possible to reduce the stress on the fish.

At a water temperature of 75° to 80° F (23° to 26° C) it takes ammonia levels about two weeks to peak and 4 ½ weeks for nitrite levels to peak. pH in new ponds tends to be very high (above 8.0). pH in ponds is affected by the mineral content of your source water, concrete or mortar in the construction of the pond, and sunlight. If you have a high mineral content in your water, the pH is typically high (above 7.8). Lime in concrete and mortar leaches into the pond water raising the pH. Water changes can help reduce the concentration of lime in the water.

Sunlight also raises the pH in the pond. When you check the pH in the pond, you should check it at the same time every day to get an idea of the stability of the pH. The pH in the morning is commonly .5 lower than the reading you will get at the end of the day. Generally, a pH of 7.0 to 8.5 is fine for most pond fish.

The higher the pH, the more toxic ammonia becomes. When you do an ammonia test, you are actually reading the concentration of ammonium and ammonia combined. Ammonium generally is safe for fish even at high concentrations, but ammonia is not. If the pH in the pond is below 7.0 the vast majority of the ammonia reading on your test result is ammonium. The ratio of ammonia and ammonium changes as the pH rises.

Nitrite is what is produced when ammonia is oxidized. Nitrite levels will begin to show up on the nitrite test kit when the Nitrosospira bacteria oxidize ammonia faster than Nitrospira bacteria can oxidize nitrite into nitrate.

Nitrate often accumulates over time in ponds. Your stocking level, live plants, algae, and anaerobic bacteria activity can affect how fast nitrate accumulates. Long-term excessive nitrate exposure can lead to health problems for fish. Monitor your nitrate regularly, testing at least once a month. Try to keep the concentration of nitrate below 100 ppm. Large water changes may be necessary to reduce the nitrate to an acceptable level. Monitoring how fast nitrate accumulates can give you an idea of how often and how much water to change.

Tip - Word of Warning

Aquarium Pharmaceuticals liquid nitrate test kit is a very popular test kit because it is very easy to use. The instructions with the test kit say to shake bottle #2 for 30 seconds. If you shake bottle #2 for only 30 seconds, you will likely get a false low nitrate reading. I recommend you shake bottle #2 for two minutes before adding it to the test sample to get an accurate reading of your nitrate content. I have seen many reef hobbyists have problems with their tank because their nitrate was off the chart when their test (following the instructions) showed near 0 ppm.

Acclimating Fish to the Pond

Ideal Water Parameters

  • pH 7.0 to 8.5
  • Ammonia 0 ppm
  • Nitrite 0 ppm
  • Nitrate 0 to less than 100 ppm
  • When you bring home your first fish, they must be acclimated to the new pond. The water temperature in the pond and the bag can be very different. Floating the bag of fish in the pond for 15 to 30 minutes will allow the fish to adjust slowly to the pond's temperature. Once the temperature has equalized, add some of your pond water to the bag and allow at least another 20 minutes for the fish to adjust to the difference in pH.

    Monitor the fish closely to ensure enough oxygen is in the bag. Once the fish are acclimated, remove the fish from the bag with a net and release the fish into the pond. Never add water from the bag to the pond, as this increases your chance of introducing diseases. It is always better to quarantine any new fish and plants before introducing them to your pond (read Pondering a Pond?).


    While your pond is establishing the nitrogen cycle, you need to feed the fish only a very small amount every other day. Ensure any un-eaten food is removed from the pond as it can increase ammonia and nitrite levels.

    After the pond is established, you can then start feeding every day. If you are feeding floating food, your new fish may not come to the surface to feed. If this is the case, you can soak the food in water for a few minutes and then squeeze the air out of the food so it will sink.

    Heavy Metal Toxicity

    Never through coins in a pond with fish. The metal in the coins can break down in the water and poison the fish and plants. Make sure you do not use any plumbing parts that are made of metal. Brass fittings and fountain heads are unsafe for ponds intended for aquatic life. Brass is a copper/zinc alloy that is very toxic to fish. Copper in the presents of zinc becomes even more harmful to fish. If your water is very soft, these metals become even more toxic. Some fountain ornaments have brass nipples to hook up flexible tubing. Ensure you do not use these types of ornaments on your pond.

    Red Dragonfly
    Dragonflies are one of the many insects that lay their eggs in a pond. The eggs and larvae of insects are a natural food source for fish. If you use algae control chemicals in the pond, you will eliminate this important natural food source.

    Alga is a normal part of your pond's healthy ecosystem. At times it can become a problem when the pond receives a lot of sunlight, the water is warm, and your pond has a lot of nutrients. A massive water change can help reduce nutrients, but often this is not enough to control excessive algae growth. The two most common types of algae that become a problem in ponds are hair and green water algae (single-cell floating algae that turn the pond water green).

    A proper pond design should include an ultraviolet (UV) sterilizer. The UV sterilizer will kill the green water when it passes by the UV lamp. Hair algae can be controlled with barley extract, straw, or pellets. There are also algae control chemicals on the market, but these should be avoided because if overdosed, they can kill fish or too much algae at once, which can cause ammonia and nitrite spikes that can kill fish. Algae control chemicals also kill many beneficial bugs that are a food source for your fish.

    The first month you have fish in your pond is the most difficult for your new fish. Testing for ammonia and nitrite on regular bases is very important and can help you avoid any fish losses. With a little knowledge about your pond's ecosystem, you should have many years of enjoyment ahead of you.