There have been many frequent questions asked regarding Koi filters as to why some Koi ponds still remain a pea soup colour even with a biological filter installed. It seems that everything is in place yet the desired result of clear, clean healthy water is not being obtained. There are a few factors to observe here that could lead to such an undesirable affect. But before we delve into that issue, I want to point out that even though the most talked about process of biological filtration is the converting of ammonia into nitrate, there is much more going on that should be made aware.

Within Koi filters, and also within the pond water, there are a wide array of biological, metabolic and chemical activity taking place, each of which is producing it's own range of pollutants. This is proceeding as organic waste, predominantly fish faeces, decomposes. The longer this waste is left to decompose, either in the pond water or in the filter, the more these harmful processes are occurring. Without regular cleaning, of both the pond water and the filter, production of numerous DOC (dissolved organic carbon) compounds are left to build steadily, increasing the level of pollutants in the water and in the filter thus increasing, and possible defeating the work of Koi filters in general.