For this question there is no general response. We have to consider several aspects of who the question posed to us and we must explain what a pre-filter is.
A pre-filter is a filter that is installed in front of the main filter. The purpose of the pre-filter is to remove dirt BEFORE it reaches the main filter.
It is very useful if you have a difficult main filter (access is difficult) or laborious (remove 80 brushes of 70cm each, which is a lot of work) to clean. Then it is a huge advantage to have a pre-filter installed and thus reduce the cleaning of the main filter to (for example) only once a week.
Another appropriate situation to install a pre-filter: When one has started “little by little” with the pond and the koi, it will probably come to the situation when the existing filtration can not cope with so many koi / big koi. It would seem likely to adapt the complete pond, but often there is neither time nor money to do it. In this situation the incorporation of a pre-filter can save the situation, because it removes a lot of dirt before it reaches the main filter and thus decongests it.
A third reason to use a pre-filter is the filter bacteria in the main biological filter. These bacteria are sensitive to cleanings. Obviously it should only be cleaned with untreated water (chlorine would kill them right away), but they are still fragile and with a strong water jet quickly thousands of good bacteria are eliminated. If we use a pre-filter, we will reduce the amount of cleaning of the main filter and let the bacteria live quietly.
A pre-filter is then advisable
- if you notice that the filter can not cope (either because the good bacteria are eliminated or because too much dirt enters). This “not enough supply” is expressed through turbid water, fish scratching, high level of ammonia etc.
- if the cleaning of the main pond is difficult and / or laborious (which in the end will result in cleaning less often and / or removing the desire to have koi)
The pre-filter recommended by Koi Hacienda is called MultiCyclone of the famous Waterco brand. The manufacturer announces that it filters 80% of the dirt that would normally reach the main filter. We can not confirm the figure, but we have very good experiences using the MultiCyclone in our facilities (before arriving at the main filter which is a UB60 filter with beads).