It can be easy to see why many people consider a pond filters sole function is to remove physical debris from the pond’s water. Most people think of a filter as a giant sieve that removes physical waste products. Whist it is the case that the filter does remove physical waste from the pond, the only waste that will be removed in this way will be the waste suspended in the water that passes through the filter via the pump. Most physical waste ands debris will just sink to the bottom of the pond and break down, polluting the water with damaging chemicals. And this is where the filter really comes into play.

The main reason you need a filter in the pond is to remove chemicals like ammonia caused by the fish and the break down of other waste products and uneaten fish food. The filter actually breaks down these chemicals using a bacterial culture. After the installation of a new filter system it usually takes around 5-6 weeks for the filter to clean your pond completely. And this is another reason why with a new pond you need to introduce fish slowly or after allowing your pond to acclimatise.