The Role of Biofilm in Koi Ponds Explained

Biofilm or bio film explained. Nitrification (the useful) bacteria are not free swimming organisms.

What biofilm does and how it works...

Biofilm is a largely self explanatory term. The nitrification bacteria that we actively cultivate in our Koi pond bio filter systems are critical to the success of any Koi pond in maintaining good water quality. The nitrogen cycle, the cycle of life in aquatic systems, is responsible for ultimate good water quality and the biofilm in which the nitrifying process takes places is critical to success.

These bacteria are not free swimming organisms, unlike many other types of bacteria (nasty bacteria that can cause disease or infection are typically free swimming).

Bio film is the term used to describe a colony of bacteria that cling to a surface. This colony is typically huge in numerical terms and limited only by the size of the surface area available.

Biofilm is extremely thin, of the order of a few micrometres thick. Current analysis suggests that the film operates in a chaotic state, with the bacteria actively jostling each other around and with fluctuating concentrations of measurable parameters making a mathematical model of biofilm extremely difficult to formulate although it's performance can be reliably predicted under laboratory conditions.

What we do know is that the process by which ammonia and nitrites are 'reacted' by the bacteria relies on a diffusion mass transfer. The thin nature of the biofilm indicates that most of it is active and that this diffusion process through the biofilm is an efficient one.

This mass transfer across the bio film is the reason why a high surface area is necessary to ensure adequate contact of pond water with the bio film. If the water passes past the bio film without being sufficiently close to the bio film, no mass transfer of the dissolved wastes will occur and the pond water will be return to the Koi pond effectively unfiltered.

Mature bacterial colonies are required to re-populate the bio film and to keep it in a state of constant renewal. Typically mature colonies are less active in munching on the waste material in the feed stream but are nonetheless critical to successfully performing biofilm.

We also know that biofilm is very rarely only composed of useful nitrifying bacteria. Chief competitors are heterotrophic bacteria which rely on organic material as a food source. Heterotrophic bacteria are faster growing and can quickly colonise surface areas faster than the much more slow growing nitrification bacteria. The only sensible way of preventing this from taking place is to remove the source of food, organic matter.

Active bed bio media is a media that due to its chaotic moving bed process does all of the good things as far as nitrifying bacteria are concerned, and all of the bad things are far as heterotrophic bacteria are concerned. This gives it a massive advantage over static media and a dramatic filtration performance boost.