Filters

[Gösta H. Lovgren]

Post here any questions or recommendations for pond filters.

[Gösta H. Lovgren]

Biological filtering is when a pond builds up a large enough biological base to keep the water clear of water discoloring microscopic algae - ie "Green Water". Note there are many kinds of algae (10's, 100's, ?) but in this thread, and generally when discussing ponds, the word algae refers to the water discoloring kind unless otherwise stated.

It's really very simple. Algae are created by sunlight combining with nutrients in the water. What happens is that as algae are formed, bacteria get formed that feed on the algae. In consistently warm water (70F+) the process from algae to bacteria takes about two weeks to a month.

Where it starts to get complicated is the bacteria are not free floating like the algae. They must anchor to surfaces in the pond. (The bottom, sides, rocks, even plants, ...). Normally, especially if fish are involved (they add nutrients to the water that increase algae load) there usually isn't enough "normal" surface area in a pond to support a large enough bacterial load to keep the pond clear.

If there is enough surface area AND there is enough circulation arcoss the surface area the pond water will stay clear. It's really just that simple.

[Gösta H. Lovgren]

Filters serve two purposes:

First is to add enough surface area to harbor enough bacteria to eat whatever algae are created. They way they do that is via the media (filter material). The more surface area per cubic inch the media has the more effective the filter will be biologically.

Second is to remove particulates from the water.

[Gösta H. Lovgren]

The simplest, most efficient, most effective filter design is a basic upflow filter. Essentially the water enters the bottom, flows up through the filter media and discharges out the top.

An Upflow Filter consists of several parts:

The Housing - can be anything water tight so long as it is large enough to do the job. Many people use barrels or drums. (One of my early filters was a 55g drum which is large enough to easily handle a 1,500g pond.) I know of people using bathtubs, sinks, milk vats, stock tanks (actually very good housings) feeding troughs, ...

Filter Media - This can be anything inorganic (won't deteriorate) that has lots of surface area and will let water pass by easily (not plug up quickly). People have successfully used hair curlers, plastic scrubby pads, spools of fishing line, ... Any number of different media.

The very best media I have found is called lava rock (It's actually coal clinkers from power plants) sold by many landscape centers. It is extemely porous and pretty cheap (under $10 a cubic foot). And lasts forever. Most/much of the media in my filter is 15 years old or more.

The Grate - The filter media sit on top of a grate that is 3" or so above the bottom of the filter. The grate ony has to be high enough to let the water enter underneath it unimpeded. It can be higher but it is sort of wasted space better utilized at the top (Floc settling area).

The Floc Settling Area - The space between the top of the media and the water discharge. Floc is the residue produced by the bacteria (akin to feces). It is very light and will settle on top of and admidst the media.

The Input - Where the water from pump goes in underneath the Grate.

The Drain - Located on the bottom of the housing. Almost the most important feature of the filter. It should be easily accessible and requires the housing be raised above the ground to provide clearance. (Some people have their drains on the side to allow the filters to set directly on the ground. And that's okay but the drain is better located on the bottom.)

The drain should be the same size as the input. It can be smaller if necessary but should be as large as practical.