There are certain other times too, besides at the time of establishment of the koi fish pond, when you need to test for the quality of water in the koi fish pond. These times are when you have added some more fishes to the koi fish pond.  These are the times when certain parameters of water will fluctuate from their normal readings. This happens because the water filter tries to adjust itself to the extra load of waste materials being produced by the increased population. So, these are the timings when the pond keeper would have to be more vigilant towards the water quality.