How to improve an existing pond filter or even make your own biofilter easily and cheaply

Selection and making improvements to any biological filter is much simpler than you think especially for small to medium sized garden fish ponds. The following points are important even if you build your own biofilter. Specification is based upon pond volume.

The size of the biofilter box or container is almost totally irrelevant .... many people will tell you that the filter should be a certain percent of the pond volume. This is quite simply wrong. Such advice will cost you more money than necessary and will not help you. Also remember big boxes can be an eyesore, difficult to hide or disguise.

The biomedium used and the flow rate through the biofilter are important to determine the size of the box or container. The table below will help you to understand the basis for selection.

This table shows that theoretically you need about 20 times more volume of foam or 5 times more volume of Lave 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 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.

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)

ALL Focus biofilters contain Alfagrog