Trickle Filters are filters that are designed for biological filtration of pond water in 'dry' mode. Dry mode filtration simply means that the filter media are not submerged underwater. Trickle Filters allow water to flow freely out of the tank by means of an overflow. As the name implies, an overflow is a mechanism that allows water to just flow out of the fish tank when it reaches a certain level. Trickle Filters reduce the nitrate level of pond water by exposing the water to a large surface area of good aerobic bacteria that consume nitrates. The large surface area is achieved by choosing filter media that has a high surface ratio. Filter media need to be fully colonized by good aerobic bacteria for a Trickle Filter to work properly. The colonization usually takes a month after the pond is filled with water. Colonization may be accelerated by mixing some 'old' filter media in with the new ones, which in effect feeds the new filter with a small colony of bacteria. In the case of the Trickle Filter, the pond water is instead allowed to drip in small streams of water through the filter media. The primary purpose of Trickle Towers is to reduce the nitrate levels of the pond water and turn green water into crystal clear water. Trickle Filters are available in different brands and sizes. For more information about Trickle Filters, please contact us.