How to Increase Pond Filter Capacity Easily

Those of you who have been reading my articles for some time will have realised that an essential component for any fish pond is a pond filter also known as a biofilter.

A biofilter has one single function... to purify fish excretions (contain ammonia) which are part of the natural respiratory and feeding function of POND FISH OF ALL TYPES.

It is not the intention of this article therefore to justify or explain reasons why a biofilter is necessary.  This article is designed to give you an intimate understanding of how you can easily and cheaply (even for free) upgrade your existing filter.

A filter needs upgrading if a lot of new fish are added to a pond (naturally or by acquisition) or as fish grow bigger, eat more food and excrete more waste as in summer.

Here's what you need to understand...

Bacteria residing on all pond surfaces including the surfaces of the biomedia inside a filter act to purify water that comes into contact with the circulating pond water that contains ammonia. For the bacteria to do a good job they need to be able to utilise oxygen also dissolved in circulating pond water.

Consider a single miniscule bacteria living on a plastic tube (biomedia) occupying space in the biofilter... A tiny drop of water comes into contact with this bacteria. Almost instantaneously the bacteria "grabs" the oxygen and ammonia in this tiny droplet and converts the poisonous ammonia into more friendly nitrates. The bacteria then waits for the next tiny drop of water to come along.

Now imagine millions of bacteria occupying space on the plastic tubes and you can understand how water, en masse, can be purified.

In simple terms the more bacteria in a biofilter the easier and more efficiently the pond water is purified. If there are not enough bacteria (eg if no filter) then ammonia builds up in the pond water and creates considerable stress on the fish in the pond.

The bacteria need a place to live and a "house" big enough to accommodate millions of them. The bigger the pond and the higher the fish stock density then the bigger the "house" must be. This "house" is a biofilter. The biomedia (eg plastic tubes) can be considered to be walls in the "house" and the more wall area there is the more living space for bacteria and thus the bacteria can multiply and efficiently do their purification job.

Different types of bacteria have different "wall" surface areas which means some biomedia types are better than others for holding large colonies of bacteria.

In technical terms we express the relationship between surface area of biomedia per unit of volume (eg sq feet per gallon of biomedia or sq. metres per litre) as SPECIFIC SURFACE AREA OR SSA.

By using a biomedia with high SSA then the biofilter will perform more efficiently. In practical terms this means biofilters filled with biomedia of high SSA can be very much smaller in size than those with low SSA biomedia.

Plastic in all forms has a low SSA and this is why filter boxes containing plastic are very large.

Compare this approximate information for different biomedia:

Plastic tubes, shavings, balls etc... SSA = 1

Lava rock ... SSA = 4

Plastic Foam... SSA = 8

Sintered ceramic (eg Alfagrog... SSA = 40

Clearly a fixed filter box size filled with different biomedia will handle significantly different volumes of polluted pond water depending upon which of the above biomedia is used.

CONCLUSION

Replacing a biomedia of low SSA with one of higher SSA will allow the capacity of any biofilter to be increased without spending money on a larger filter. That's all you need to do to maintain a high efficiency biofilter.

If you're making your own biofilter this information can save a lot of money and makes hiding of a biofilter much easier because the box is much smaller.

WHAT IS BEST BIOMEDIA FOR STATIC BIOFILTERS?

 I have no doubt whatsoever based upon 15 years experience that Alfagrog is the best biomedia. As you can see above its SSA is 40 times more than plastic.

In the USA you can buy Alfagrog (its called SUPRA in USA) at Macarthur Water Gardens in Florida... here's the link to Macarthur

In South Africa you can buy this low cost biomedia from us at Superpumps... 

In the UK I'm not sure where it can be bought.