Beware of Pond Filter Tales That Bear No Resemblance to Fact or Logic

A couple of weeks ago I was doing a talk at a large customer's store to interested pond keepers. There was a good sprinkling of koi keepers were there also prior to the annual koi auction. Koi are very special fish and koi keepers do tend to take a greater interest in what is actually happening beneath the surface of their ponds more so than the casual gardener.

Before the talk got under way I found myself in "discussion" with a koi keeper on biofilters. It wasn't long before a minor confrontation developed around biofilter size. For the umpteenth time in my life I heard the FACT that a filter had to be 1/3 the pond size whatever that actually means.

The other party was not impressed by my views and once my talk started there was one less listener.

Let me try hard to debunk this myth of biofilter size and explain what is really really important. If there is a need to talk about size at all then this must relate NOT to pond volume, NOT to filter box size, and NOT to relationships between pond volume and filter volume.

Size in terms of effective biofiltration ALWAYS means size (rather speak of quantity) of surface area where the bacteria, oxygen and food source come into contact with each .... ie at the biomedia surface.

Of course we all talk of a biofilters being suitable for a pond up to x gallons because we have to try and simplify the understanding for both sellers and buyers of off-the-shelf products. And of course we all generalise in order to communicate "better".

There is a product called Flocor which is sold around the world as a biofilter medium ... a biomedium is a place where bacteria can happily live by clinging to a surface that comes into intimate contact with water containing nutrients and oxygen. Flocor is one of thousands of possible media. They have just done a great job of marketing their product over the years. Just in case someone does not know what Flocor, let me describe it ... it is a hollow black plastic tube with a few ridges. It is about 1 inch diameter and 2 inches high, normally black.

The ridges by the way are cosmetic to all intents and purposes. Flocor looks similar to any other simple plastic tube with minor ridges and is not better than any other ordinary plastic tube with or without ridges. And the fact that it's black is not important.