How To Select A Fish Pond Biofilter?

Why You Need a Biofilter and How it Works

It’s important to realize that a biofilter is needed to purify the pond water… Fish pollute the water through natural metabolism. These nitrogen based toxins reach lethal levels if not removed A filter is also useful to remove suspended solids from the water.

If your pond is small to medium and you do not intend to stock with expensive fish then there is little need to overspend on a biofilter with all the bells and whistles and hype. Price is not the determinant of how good the filter is. Your choice will be between a gravity (box type) filter and a pressurized one. No matter which kind you select it is the biomedia that is important.

There are 3 kinds of biofilters that would be suitable for a pond, water feature or even a swimming pool. These biofilters are namely:

  1. Gravity Flow Biofilters
  2. Pressurised Biofilters
  3. Bubble Bead Biofilters

Gravity Flow Biofilters

Low cost gravity flow biofilters are used in any size pond. The picture is of a range gravity biofilters available. These filters can be supplied with two types of biomedia… either (1) Bio Balls which are 40mm square plastic components specially made for use in low pressure biofilter systems or (2) Alfagrog which is a high efficiency biomedia developed in the UK for the fish farming industry.

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View our range of Biofilters and Alfagrog here.

Alfagrog is a sintered ceramic material which means it is extremely hard and porous yet does not break up. These units can be piped up in parallel for very large systems making them suitable for any sized pond. With the very high electricity cost these days ponds operating with sand filters should seriously consider changing to this type of filter… Such a change will save many thousands of Rands over the life of a pond.

Pressurised Biofilters

Pressurized BiofilterPressurized filters can be easily hidden or located some distance from the pond itself. Cleaning is easily accomplished by using the nozzles available. Pressure biofilters need an extra powerful pump head to push the water through the system.

Pressure filters are almost always sold with an Ultra Violet Light combined with the pressure filter itself. This is to ensure crystal clear water is achieved and to make installation of the combo unit easier.

Follow the recommendations in the pump selection page to specify a pump and if any doubt go at least one size larger.

The principles behind correct specification are the same in all filter types.

The Bubble Bead Biofilter

This is a type of Pressure Filter. Only for use on larger ponds eg 100,000 litres. Not for the average pond keeper!
An important point to note is that the Bubble Bead Filter is both a mechanical (removes solids) and biofilter (removes dissolved ammonia and nitrites). It is not designed to be used on smaller garden ponds.

Pond BiofilterA relative newcomer to the South African pond keeping scene is the highly efficient Bubble Bead biofilter. This filter works on the principle that the biomedium (ie the surfaces on which bacteria live and grow and carry out the action of converting dissolved ammonia ultimately to nitrates) is agitated and kept in suspension… what this simply means is that owing to the agitation or turbulence in the filter it becomes possible for a relatively small amount of biomedia to convert much higher quantities of nitrites and ammonia because the turbulence ensures that the bacteria on the surface of the biomedium always have a new and fresh source of ammonia or nitrites “to eat”. In other words the efficiency of these biofilters is extremely high and they can be sized to be used on ponds from small to very large.

The Bubble Bead filter works under pressure in a closed environment. They can be used on small ponds up to the very largest fish ponds (including commercial breeding ponds).

The Bubble Bead filter makes for a very compact and neat configuration and is the lowest maintenance pressure filter available. These filters are sized to handle up to 100,000 litres of pond water.

Adding to the extremely high efficiency of this biofilter is the fact that the blower not only increases pond aeration but assists in the backwash of accumulated debris on the bubble bead surfaces.

The efficiency of this pond filtration system is further enhanced by the use of a bio-booster containing the highly efficient biomedium Alfagrog.

Bubble Bead filters are low maintenance mechanical filters as well as highly biologically efficient biofilters due to the intense agitation involved… in chemical engineering terms the effective surface area for ammonia conversion is extremely high.

In summary Bubble Bead filters have the following advantages:

Occupy small area relative to filtration efficiency
Low maintenance operation
Highly efficient biological removal of ammonia and nitrites
Effective mechanical solids removal filter system

You Must Know Your Pond Volume… That’s All Really

To specify an appropriate biofilter it is important to know the volume of water in a pond to about 80% accuracy. A filter is specified in terms of what capacity it can handle when the pond is stocked normally. The greater the mass of fish in a pond the greater the level of pollutants (because more food is fed) so a larger filter would be used.

How to select a biofilter

A filter will claim to handle or purify up to 5,000 litres of pond water. The claim will be based upon qualifications such as fish stock density, amount of food fed and so on. If you can afford it always go slightly bigger to get better performance.

A biofilter will NOT clear a murky pond caused by suspended algae without help from an UVC (Ultra Violet Clarifier). Many modern biofilters have a built-in UVC. This is a good choice of filter to buy.

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