As a child I remember having several goldfish over a period of time. I used to keep them in a goldfish bowl, where I used to watch them feed on the goldfish flakes that Mom bought for me. The strange thing was they never seemed to live a long time. I never understood why! It was only as an adult after I had become hooked on water gardening that I learned the secret of their demise. It was due to ammonia poisoning. Unbeknown to me at the time I was sealing the fate of the poor goldfish by trapping them inside of a bowl where they had to eat and go to the toilet. They had no way of escaping the gradual build up of ammonia.



In a garden pond, even though there is a larger volume of water than in a goldfish bowl the level of ammonia build up will increase significantly, particularly if you have plenty of Koi, which are voracious eaters. The only way of preventing a constant build up is to remove it as soon as it is released into the pond water. The most effective method is to use a pond bio filter.

How Does a Pond Filter Oxidize Ammonia?

In the biological chamber of any successful garden pond filter you will find the following key components: a source of food (ammonia); nitrifying Nitrosomonas and Nitrobacter bacteria (the dinner guests) that oxidize ammonia into nitrates and plenty of oxygen. Oh by the way did I mention oxygen? Oxygen is absolutely critical to the nitrifying process. Without it the oxidization of ammonia will not be able to take place. It creates turbulence which provides the optimum conditions for ammonia break down.

The chemical process responsible for the conversion of ammonia into nitrites and then into nitrates is known as the Nitrogen Cycle or Nitrification Process and continues within the biofilter chamber 24/7. This process will only stop when you switch your pond filter off or if the pond filter stops working. Warning! Don't switch the pond filter off. Nitrifying bacteria require a constant supply of oxygen. If they are starved of oxygen for more than 5 hours they will die. This renders your pond filter pretty much useless until the bacteria colonies have had time to build up again, which can take up to 5 weeks. In the mean time you will have to carry out frequent water changes and ensure that you do not overfeed your fish. You will also have to constantly measure the pond ammonia levels, using a suitable test kit.

Factors Affecting Ammonia Levels in Garden Ponds

* The type of fish you keep in your pond and the numbers stocked will have an influence on the levels of ammonia in the pond water. Koi are ravenous creatures that when healthy will eat as much food as you feed them. This obviously has a major impact on pond water quality; not only in terms of ammonia levels but also upon levels of heterotrophic bacteria that cause fish diseases. You will probably be more familiar with the rotten egg smell than the term. Heterotrophic bacteria release Hydrogen Sulphide, the cause of the rotten egg smell.

* If you have a pond that hasn't been routinely cleaned from time to time and where rotting vegetation has been allowed to accumulate on the pond floor then ammonia levels will be higher. Decaying organic matter releases ammonia into the pond system.

* The quality of the fish food and the amount fed will also influence the ammonia concentrations contained within the pond water. Always feed low ash content branded fish food that contains protein, vitamins and trace elements. This high quality fish food will allow your Koi to use up more of the food to grow and develop, rather than excrete it into the pond in the form of ammonia.

How Can I Improve The Effectiveness Of My Pond Filter?

You will need to maximize the potential for nitrifying bacteria, oxygen and ammonia to be in constant contact. In practical terms the following suggestions will significantly improve your pond filter performance:

* If you currently use plastic coils, hair curlers or any other plastic media and have a box type filter or compact pressurized biofilter then over a period of time replace it with a superior filter media that has a much larger surface area. One of the best low cost options in the USA is Supra filter media, known as Alfagrog in the UK. Have a look on the web for the nearest stockist to where you live or try your local pet store or aquarium stockist.

* Pump as much oxygen into your garden pond as you possibly can. Add a water feature, waterfall or pond aerating pump. A water feature or waterfall will not only add much needed oxygen but will also add the sound of flowing water and make a great focal point.

Buy a pond net and scoop out any floating leaves, grass and uneaten fish food on a regular basis. Basic housekeeping such as this will remove the potential for pond debris to rot on the pond floor. Rotting organic matter produces ammonia.

The secret to successful pond keeping is to read as much as you can about your hobby and to learn from mistakes. The internet is a great source of information and there are many water gardening forums where you will readily get answers to many of your questions. The last bit of advice I would like to offer you is to ensure your garden pond has a plentiful supply of oxygen and that you don't overstock your pond with too many fish, particularly Koi. One last thing buy a master pond test kit and regularly monitor the pond water levels for pH, ammonia and nitrate. By frequently testing the quality of the water you will get to know your pond better and will become familiar with the various fluctuations in reading that take place. If you notice anything out of the ordinary then this may be an indicator that something is wrong.