The choice of bio media may seem an unimportant one but little could be further from the truth. Your Koi pond relies on its filters to ensure continous purification waste water from the Koi pond and your bio filter plays the single most important role in this process.
Without a good bio filter your chances of a successful Koi pond are greatly diminished. As such the choice of biomedia for your biofilter is important.
As with most things there are pros and cons to various types of media. Loosely they can be broken down into two broad categories - static and moving bed.
Static media comprises of the vast majority of media available today. Japanese matting, bio balls, volcanic rock, cut hair curlers, plastic shavings, you name it. Anything that can be packed falls into this category.
Static media all suffer from a majr drawback - that of channelling. When water enters a filter, it heads for the exit along the quickest path of least resistance.
Think of the way water flows when your filter is empty and it fills for the first time. As water fills the vessel, all media is placed into contact with water that needs to be filtered coming from the Koi pond.
And this is important. Once the vessel is full the water flow patterns change dramatically. Once the vessel is full, water will take the quickest and easiest path from entry to exit that it possibly can. In other words, water will pass in a roughly straight line directly from the entry point to the exit point.
People have tried several fancy designs to overcome this issue. Such complex systems can improve flow patterns by a few percentage points but in most cases where you have static media packed into a vessel the incoming water can bypass between 60% and 85% of the media.
Hence, you need to have more media in order to achieve overall performance of your bio filter.
Static media is also prone to clogging. Some static bio media installations can become a maintenance nightmare requiring frequent cleaning.
Moving Bed Media
Moving bed media on the other hand has no such constraints. A moving bed moves, thereby disrupting water flow patterns and making channeling impossible. Whilst the media tumbles and churns within the biofilter, each individual media element is able to make contact with the water in the filter on a continuous basis. This means that the biofilm growth on each element is similar.
There are other advantages. It is a self cleaning media which will last for many years to come. It operates in an oxygen rich environment thereby not stripping oxygen from the incoming water stream in the oxygen intensive nitrification process.
SuperActiFlo as a moving bed has a zero head loss. In other words there is no pressure drop across the moving bed. Hence very efficient water movement systems can be achieved with minimal power usage.
There are of course drawbacks. SuperActiFlo requires some care to install to prevent the media from escaping the bio filter vessel. It also is a 'open to atmosphere' media - so in some instances where only pressurised vessels are used SuperActiFlo will not be appropriate. Also some care needs to be taken with airlines delivering the air bubbles if you are using it in a DIY installation.
These are not significant drawbacks however and SuperActiFlo is becoming adopted by many Koi pond keepers because of it's numerous advantages.