Garden pond and water feature biofilters clean ponds

Pondkeeper's How to...

Garden pond and water feature biofilters

The main reason for a biofilter in a pond is NOT to filter the solids out of the water. It is to purify the water by removing offending chemicals.

These chemicals, starting with ammonia, are actually produced by the fish themselves by virtue of their normal breathing, eating and toilet behaviour.

Pond biofilters need a continuous supply of oxygen. The source is dissolved oxygen in the pond water continuously circulated through the pond biofilter. This is why a pond pump supplying any biofilter must run 24 hours per day

Make access to your pond biofilter easy. If there is a risk of the pond's biofilter overflowing and emptying the pond in the process then try to ensure the overflowing water would find its way back into the pond. This risk is real for most biofilters - if the outlet from the biofilter blocks then the pump will cause the water to overflow through the biofilter lid.
Brushes are often used in pond biofilters. Ask yourself why do you use brushes?

Do you really need them ... possibly not. They do add to the cost without creating a major benefit in most small pond biofilters. Brushes in off the shelf conventional pond biofilters have such big gaps in them the only purpose they can serve is to remove long stands such as twigs, lengths of algae etc. For this purpose they are obviously fine .... is this what you want to achieve? For any other reason they are unsuitable. They don't do any harm ... they just make you a bit poorer.