Some tips to consider if you decide to build your own pond biofilter 

Spring is almost here

Do yourself a favour this year if you already have a pond and especially so if you don't but intend to install one. Add some really useful bio capacity to your biofilter. Last years fish will get bigger this year, many ponds will have new-borns soon and these add load to your filter. This is something many people do not realise until it is pointed out.

A biofilter is a box full of biomedia with water coming in one end and going out the other end. In its very simplest terms that is exactly what it is. For most garden ponds that's all you need ... promise.

Do not get carried away with the sales blurb you will come across ... our filter is bigger so must be better implication, has 12 brushes not 10, 3 layers of foam not 2, three different sponge colours and so on and so forth. These are schemes to part you from your money whilst doing no harm I must hasten to add. In fact ignore most of this hype ... unless you truly understand the meaning behind the claims.

Below is an article I wrote for my South African edition in December which I have modified a little for International audiences so ignore references to R for Rands. Unless you are a serious large pond or enthusiastic koi keeper involved in growing large fish for exhibition purposes you do not need to spend hundreds and thousands of $$$$$ even. You need to spend far less than $100 ... even $20 if you are DIY inclined.

Where I use the word Alfagrog below you can substitute plastic tubes, hair curlers, rocks, and any other medium you wish to use as the surface on which the bacteria will grow but just remember you will need CONSIDERABLY larger volumes of other materials and therefore a larger box. But on this subject of Alfagrog I have also good news .... I have finally found a source of VERY low cost commercial biofilters in the USA that have Alfagrog inside them. It is just not called Alfagrog .... click the link to the right to learn more. Alfagrog is a magical biomedia and is also a good mechanical filter too. And it is cheap.

GARDEN POND BIOFILTERS ARE NOT COMPLEX

This table shows that theoretically you need about 20 times more volume of foam or 5 times more volume of Lava Rock to do the same job as a single unit of Alfagrog ... in other words if you need 2 litres of Alfagrog you need 40 litres of foam and 10 litres of lava rock. The practical and cost implication of this is that you need a MUCH smaller lower cost container for a biofilter containing Alfagrog than other media such as plastic tubes, foam, lava rock, hair curlers and so on.

Making a biofilter is very simple and it will be as effective as most shop bought products, probably better ... see opposite

Some tips to consider if you decide to build your own pond biofilter ..

1. Up flow through the bed of Alfagrog or any other biomedia is best ... in this case it is also an improvement to create an empty space at the bottom of the container into which the pumped water first flows (use a plastic crate section or something similar) to create this void ... any solids can then tend to settle out before the water enters the bed of Alfagrog

2. Put the Alfagrog inside a string bag to make removal quick and easy for cleaning purposes. Clean as often as you like buy always use pond water.

3. By using Alfagrog there is no need for any foam or brushed inside your filter.

4. Alfagrog costs about R22 per litre so for around R100 you can build an effective biofilter for a pond of about 1,000 litres. Even for a 5,000 litre pond cost should not exceed about R350.

4.5 litres is 1 UK gallon approx

3,8 litres is 1 US gallon approx

In simple terms the biofilter contains media on which a large amount of specific bacteria grow in order to digest the pollutants created by fish bodily wastes building up in the pond water. This is the very principle on which all biofilters work ... use more biomedia and you get better biofiltration capacity ... simple as that Think of the bacteria as clinging to all possible surfaces in the biofilter box. This means the more surface there is then the more can the amount of bacteria be ... simple as that. The surface comes from media with rough porous surfaces (not smooth plastic or stones) and this is what creates large areas of surface. We talk of SSA ... specific surface area... Look for biofilters which contain biomedia with high SSA as in the following table ..... Alfagrog porous ceramic biofilter medium is the best and it is low cost

Work on using 2 litres of Alfagrog per 1,000 litres of pond water.

How To Make Your Own Bioflter

1. Buy a suitable container large enough to hold the Alfagrog .... Addis and SA Leisure (in South Africa) make superb low cost black boxes (including lid) which are available at most hardware stores

2. A container of about 20 litres is sufficient for ponds up to 5,000 litres (but ONLY if Alfagrog is used). If you use plastic rings or similar items you will need at least 200 litres container and possibly more for a 5,000 litre pond.

3. Create a water inlet (at bottom or top) and a water outlet .... outlet must be at least double the diameter of the inlet. If your water inlet is at bottom (preferred) then outlet must be at top and vice versa because the water pumped into the biofilter must pass through the complete bed of Alfagrog. Make inlet about 20 to 25 mm and outlet not less than 50 mm diameter. If you find outlet too small, make a second one or increase size of first one. You will know if outlet is too small because the biofilter will overflow. You can also reduce the inflow to achieve the same effect ... do NOT allow your biofilter to overflow (you will empty your pond).

4. To make the inlet and outlet connections nice and neat use what are called Tank Connectors ... ask your hardware store or look for a pipe fittings supplier in your area.

5. The alternative to tank connectors are simple lengths of pipe going through the sides of the container and glued into position. The inlet could even be achieved by cutting a semicircle into top edge of container on which inlet pipe can rest .... use a right angle bend and short length of pipe to extend pipe to bottom of container if you want flow upwards (up flow is best)

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