How a correctly designed Biofilter can save you money on a pump

I am sure you are saying to yourself how on earth can biofilter design effect the cost of a pump? Here is the relationship between a biofilter and the pump. If you have a biofilter with lots of bio media inside it then you need lots of water flow just to cover the bio media

 If you need lots of water flow then by definition you need a larger size pump.

If you have a small flow of water to a larger biofilter than the following happens ... The water finds its way down certain parts of the bio media and not others.

This is typically what happens in a sand filter but it can also happen in any biofilter with any other bio media where water flow is insufficient to cover the media. This is called channelling. In anaerobic areas of the biofilter where water flow is insufficient two things happen.

Any oxidising bacteria in those areas will be devoid of oxygen and will die. Anaerobic areas within a biofilter breed anaerobic bacteria which are potential disease problem sources. There is however a potential benefit and that is that nitrates will probably be reduced because there are bacteria in the system that reduce nitrates to nitrogen gas (this is called de-nitrification).

You can see then in principle that the smaller biofilter made possible by using efficient bio media can have smaller flow rates through it because it is easier to ensure water flows across the complete bed of bio media.

Because of the above reasons it is always better to have a biofilter were the water flows up through the bio media. In general more water provides better biofilter action.

Please note despite the above discussion it is always a good idea to pump sufficient water around the pond to change the contents approximately 8 to 12 times a day.