Plant Doctor Archive

Water Gardens — Pond filters

WHAT is the difference between a UV filter and a biological one?

A BIOLOGICAL filter is essentially a sewage treatment station for your pond. It relies on beneficial bacteria known as nitrifying bacteria to process the fish waste from the harmful form that comes out of the fish (ammonia) to the relatively harmless form that is used by plants (nitrate). This process is called nitrification and is the basis of all good filter systems.

A UV filter on the other hand kills the algae that cause green water. Used together, and properly installed and operated, these two units (which are often sold as a combination unit) will guarantee you clear water.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.