Nitrogen cycle in ponds

Relaxing by a tranquil pond, listening to the trickle of water and visually drinking the color reflections of lillies is a busy man's dream. Cleaning, fixing, treating, and generally slaving to keep a pond beautiful is a nightmare.

The secret to maintenance-free ponds is in developing a healthy, balanced ecosystem that virtually takes care of itself.

Ponds, like aquariums, need a little help to get started. Unlike aquariums, it is easier to develop the care-free ecosystem in a large volume of water than in a small tank.

Begin by understanding the cycling process.

 (See the nitrogen cycle image above)

  • Filling the pond with water (or even topping it off as it evaporates) introduces dangerous chemicals into the water. Chlorine and Chloramine are toxic to fish and not healthful for plant growth. Some water even contains heavy metals. Always treat new water with toxin-neutralizing products.
  • Now that you have clean, toxin-free water, you need to start some beneficial bacteria growing in the pond and in the filter. Anarobic (oxygen loving) bacteria literally eat and digest organic waste products, turning them into nitrates and fertilizers for plants.

How to De-Toxify Waste - GOOD Bacteria & BAD Bacteria

There will be plenty of waste to de-toxify. Fish eliminate in the water and plant material and excess fish food fall to the bottom and decompose. If not properly turned into beneficial products, your pond will putrify and die.

Several products contain beneficial bacteria with which to seed the pond as well as enzymes to speed the decomposition process. (enzyme and sludge-removing products will be used regularly to enhance the natural cleaning of your pond)

  • Bacteria cling to rocks, stones, fixtures and to your filter media. They need a large surface area over which the water (carrying its pollutants) can pass. Your filter contains a pre-filter pad that traps large particulates and debris (which you should clean frequently). The filter also contains other materials on which the bacteria grow. Do NOT clean this portion of the filter unless absolutely necessary, and never clean it with chlorinated water. That kills the bacteria you have worked so hard to establish.
  • Now that you have introduced bacteria, you must give the bacteria something to eat so that they can "live long and prosper". Begin to add small fish and plants.
  • The water may be cloudy at first because of already-present bacteria death. The particulates and bacteria that make your water cloudy can be removed by adding water clarifiers that will "clump" the cloudy molecules together and allow them to sink to the bottom or get trapped in the pre-filter. Beneficial bacteria feed on the decomposing molecules of cloudy water and turn them into beneficial products.
  • During the first few weeks, before the bacteria has become settled and multiplied, you'll need to test your pond's water quality frequently. Too much organic decay and too little bacteria can lead to a high ammonia level which is very toxic to fish. A good all-around water test kit for ponds or aquariums will be needed. (do not use a swimming pool or hot tub kit)
  • Ammonia "burn" damages fish gills and scales. Several products may be added to the water during the "cycling" process (or any time you suspect high ammonia or stress) to help prevent damage to the fish from ammonia build-up. They are a good maintenance treatment any time you are adding water or otherwise adjusting your pond's water quality.
  • Adjusting the pH of the water is also important. Pond fish generally thrive in neutral to soft water - water whose pH is at 7. Your test kit will allow you to see the pH. Several products are available for adjusting the pH of the water.
  • Fish also need electrolytes - especially when they are under stress as when being introduced into a new pond or waking from a long winter's hybernation. Adding Pond Salt will give them a Springtime boost. (If you have water plants, you may skip the salt as some plants do not do well in salted water.)
  • If the water begins to turn green, algae may be blooming in your new ecosystem. Too much sunlight, too much fertilizer, too few plants. Adjust these factors or add a UV filter to the system. (See our other articles on algae control).
  • As your pond settles into its cycle, it will become more and more stable and care-free. The most important maintenance procedure that should be preformed routinely is cleaning the pre-filter and dragging any debris or sludge from the bottom. Plant materials, leaves, lawn clipings etc blow into a pond over time. Use sludge-removers to speed the decomposition, and manually dredge the pond once or twice a year to remove the majority of the build-up.
  • See our pond-building tips below and our other articles on Springtime Pond Start-up and Winterizing Your Pond as well.


  1. Start by making a list of the goals for your pond.
    • Do you want it to be visible from a window in the house, effectively bringing its tranquility indoors?
    • Do you want it to be away from the attraction which draws its visitors through your meandering garden to a secluded hide-away?
    • An attraction visible from every corner, or an addition to a patio or barbecue area?
    • Do you want fish in the pond or just plants? Do you want your fish to "winter over" outdoors and do you live in a cold or temperate climate? (You must make your pond deeper for fish in cold climates but can make it more shallow for warmer ones).
    • Do you want a fountain, trickling or spraying?
    • Do you want lilies or open surface?
    • Do you want a regular or irregular shape?
  2. Visually survey your property. Make a scaled aerial view map of the area, noting where trees and garden areas already take up space, and then make dotted lines where you intend to build other structures or denoting the adult width of trees already planted or intended.
  3. Avoid tree-shaded or potentially tree-shaded areas if you wish to plant lilies in your pond. The lillies will thrive in the direct sunlight and shade the water surface from the UV light which is conducive to algae growth. Trees can provide too much shade and also present a nuisance when they shed their foliage into the pond.
  4. Note outlets for water and electricity that are already in place.
    • Are there building restrictions which might affect your plans?
    • Easements?
  5. Do you know the soil consistency?
    • Clay?
    • Rocks?
    • Limestone?
  6. Draw the pond area to scale on your map, including its shape.
  7. Gather your tools.