How to carry out a partial water change.

As koi keepers we are experts in keeping fish in an enclosed artificial environment that is stocked with an unnaturally high stocking level and fed a relatively large quantity of food. Consequently, there will come a time when the pond's ecosystem becomes unbalanced, requiring our input and intervention (yet again).

Yet over a longer time frame, (weeks and months), our pond water will naturally start to accumulate a multitude of other processed by-products that if our pond was natural, would simply be processed further and taken up by other living organisms in and around the pond.
These intermediary compounds are quite safe at specific concentrations in a pond (usually measured in parts per million) but over time, could accumulate to levels that would begin to adversely affect our koi directly, or indirectly by unbalancing the pond environment.
Another reason for carrying out a partial water change is to add minerals to a pond that may not have had the benefit of regular clay treatments.
You can use a combination of information gained both visually and by your test kit to determine whether your pond would benefit from a partial water change.
This is the 'bank' where the nitrogen from the ammonia is ultimately deposited, increasing in concentration as more nitrite is oxidised into nitrate by bacteria in the biofilter.
Other cumulative compounds (sulphates, phosphates etc) will have a tendency to accumulate but rather than test these individually, use the nitrate test as a useful benchmark (i.e. if the nitrate levels are increasing then it is highly likely that the others will be also).
The water purifier will intercept and retain any undesirable contaminants in tap water that will also accumulate in your pond, causing stress to your fish.
The alternative to using tapwater that has been passed through a purifier is to add a quality tapwater conditioner to raw tapwater.

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