The nitrogen cycle

It is important to appreciate that a pond differs from natural bodies of water in two fundamental ways.

Firstly, ponds do not receive a constant supply of fresh water to replace the 'lived in' water that they contain. Secondly, most artifical ponds have a far higher stocking level and bioload (the sum of all the biological activity going on) than natural ponds and lakes. For these reasons, you as the pond keeper must be aware of the nitrogen cycle and how to maintain it at a healthy equilibrium.

• Chemicals should only be used in the Koi pond to cure known health problem, never as a matter of routine. Medications can never replace good management, and there are no miracle cures.
• Calculate your pond gallonage accurately in advance, overdosing can kill; underdosing fails to work.
• Always follow the instructions on the container of any pond remedy. The dose level of a medication is based on its concentration, which does not appear on the bottle, and will vary with the brand. For example, malachite green and formalin are both availble in variable formulations, so using some brands at the generic dose would not be appropriate.
• Test the water to ensure that all parameters are normal before introducing a medication. If ammonia or nitrite is already polluting the water, a chemical will make matters worse. A pond treatment used in a pond in which the pH has fluctuated could kill all the Koi. Re-test the water following treatment to ensure that the filter is still biologically effective.
• Switch off the UV whenever chemicals are used, as it can weaken their effectiveness.
• Ensure oxygen is adequate before using a pond medication. The dissolved oxygen level will become lower as the water temperature rises, and chemicals will lower this even more. It is advisable not to treat the pond on a hot day.
• The argument for switching off the pond filtration system while using a medication is a negative one. The presumption is that it will prevent loss of filtration biology due to the action of the chemicals. However, consequences of a die-back in the filter due to the reduction in oxygen supply could well equal any loss attributable to the chemical. Filter media will all vary in this respect, as some, more than others, will have the structure to best protect the organisms during the presence of a chemical. Bypassing the biological filter during a treatment is yet another possibility, but this too can only work in the short term. If sequential treatments are required, the filter will be bypassed for so long that some die-back will be inevitable. Some stages in the life-cycle of certain parasites may well be in the filtration system anyway, although this depends on the organism and the way the filter is designed.
• Aways measure a pond treatment into a watering-can (kept exclusively for pond use) that has been pre-filled with pond water. Then distribute evenly all around the pond.
• Many of the products used in fish health are toxic to humans. Disposable gloves and protective clothing are recommended; the eyes, too, are vulnerable. Those with asthma or who are concerned about resiratory problems should wear a mask, particularly when dealing with powder products, or when formalin is in use.
• Store all the chemicals used in Koi keeping with lids secured, away from children and pets, and in a location where it is cool, dry, and dark.
• Many chemicals become either toxic or ineffective with age, so check the shelf-life with the namufactures. Test kits, too, can give a false reading if out of date.
• Allow time for chemicals to break down before repeating a treatment, or using an alternative product- with most chemicals this takes from three to seven days. Never mix products without checking safe combinations.