When you visit for example a Koi show, you always see a high variety in filter systems: sieves, drum filters, trickling filters, chamber filters, bakki showers, moving bed filters, bead filters, you name it. They all have the same purpose, and that is filtering the water. But what exactly is filtering and why is it so important to filter your water? What kind of filter is neccesary for my pond? Well, it is not that difficult to find out, but unfortunately widely unknown….
For example a pond of around 20 cubic meters, what kind of filter is needed and how many Koi can you keep in this kind of pond? When you ask this question to ten different persons, than you will receive ten different answers. In this series of articles I want to explain how we keep the water quality in our ponds at a good level, and that quality control can be done with the use of several important guidelines.
Because filtering, why do we need it? What is the main reason for filtering the water? Many people would say: “to maintain the water quality at a good level”. But what is water of a good quality? Is tapwater the standard for good quality? If this is the case, how can we keep the water in our ponds which is filled with a high density of Koi (that receive a high protein diet every day) at a ‘good’ level?
A filter it is then! This filter exists of two main steps: a mechanical (prefiltration) and a biological part. Prefiltration is often done with sieves and brushes and recently the drum filters are introduced in the Koihobby. This mechanical filteration is neccesary to remove a range of particles (f.e. leafs, uneaten feed and feaces) out of the water. When this is not installed, the solid waste will sink to the bottom and break down, this process will increase the oxygen demand of the water. Further, particles can have a bad influence (reduced efficiency and clogging) on the biological filter, so the mechanical filteration will keep the biological filter ‘clean’. This is important because the biological filters consist of nitrifying bacteria. These bacteria convert the Total Ammonium Nitrogen (TAN) into NO2 (nitrite) and in the end into NO3 (nitrate). TAN is a term that is often used in the aquaculture for the amount of NH4 and NH3 together. This change is important because TAN is a waste product of digestion and it is toxic for fish. The intermediate product in the nitrogen cycle (nitrite) is also toxic, however nitrate is only toxic with a very high concentration.
It is thus important that the biological part of the filter stays clean from solid waste; otherwise a kind of competition will take place between the heterotrofic (bacteria which need a substrate like uneaten feed and feaces) and autotrofic nitrifying bacteria. When there are many heterotrofic bacteria, there is less space for the autotrofic nitrifying bacteria, so the filter will drop in efficiency. The work of these autotrofic nitrifying bacteria is illustrated in the nitrogen cycle below. Unfortunately this is in Dutch, but I think the pictures will help a lot. Otherwise you can also search on the internet for the ‘nitrogen cycle’.
Well, now we know how the waste is managed in our pond. In a following blog, I will complete the picture and explain more about ‘how to anticipate to manage the pond in a proper way’.