Pond Tips - Filters for Tiny Ponds page #2

Tiny ponds, those smaller than 300 gallons do not require expensive filtration systems. In fact an excellent filter can be hand made at very low cost from easily aquired materials. You will need a pump to move the water, and something on which to accumulate the debris and remove the dirt from the water.
A stiff frame is needed to create the filtration space and coverings are needed to allow you to clean the filter with as little effort as possible.
The best method that I have developed to date is to construct a cage into which the biological portion of the material is held. A pump is installed within the Bio media and the cage gets two covers. The first and mostly permanent cover is made of a screen, we use plastic window screen material. The second (Outer) cover is made of a dense pile fabric that resists wear. Our favorite is a nylon grid base covered with very fine Dacron fibers. This cloth can last for two seasons if handled carefully.

We start with a non-rusting strong fence wire that is rolled into a cylinder. A short length of plastic hose is attached to the pump outlet and this assembly is placed into the cylinder (fence cage). The pump outlet hose will extend beyond the finished filter.
Water will be drawn into the cage, into the pump and exhausted out of the plastic hose. The cage is now covered with the screen material and packed with the Bio media.
This Bio assembly is best left undisturbed over time, to protect the Bio culture that will grow within, so it can be semi-permanently closed. We have used numerous materials for the Bio media. K1, scrubbing pads, balled up screen, pieces of Matala left over from big filters, etc. There is no need to spend big bucks, just pack the cage fairly densely with the material available and close the screen bag around the outside of the cage with the hose protruding.
The second (outer) fabric bag is placed over the cage now and tied around the extended hose/electric cord. You now have an excellent biological filter for a tiny pond. It's that simple. When the flow gets reduced due to dirt on the cloth, remove the outer bag and hose it clean.

Now lets take it a step at a time to talk in greater detail about construction. If you are not quite comfortable working with hand built projects, it's best to buy the materials one at a time as you proceed. This eliminates the "Uh Oh it's too short" that happens all to often. Murphy's Law has a sneaky way of messing things up. Remember, one step at a time and "Measure Twice - Cut Once" is always a good rule.

To determine how big the filter must be, think 5-10% of the pond volume as ideal. In a 300 gallon pond that would be 15-30 gallons. It is easiest to make a cylinder, but often a rectangular box will work best, especially in shallow ponds. The shape does not matter, but a box becomes more complex to create. Before you go that route, consider a milk box for the structure. You could even place potted plants on top of those when finished. In all cases, the finished filter should be placed to allow water to pass thru as much area as possible. Laying the filter on the bottom could block a whole surface, so prop it up on something.

One caution, light fence wire WILL NOT hold up to the suction of even a small pump. There will be a lot of square inches of surface inside the cage. A suction of just a couple of pounds per square inch can become a great force when multiplied by this large surface area. We have seen customers come here with wire frames that were reduced to a handful of twisted wire, fromjust such force. Select a fence wire thickness that you can barely bend by hand and use tools to shape it.
These small filters need occasional cleaning of the outer bag, so keep that in mind as you formulate it's size and shape. Two smaller filters may prove more sensible than one large one and two small pumps are usually the same cost as one larger one. When we build cylindrical frames that will be standing tall, we set them in planter drip trays of the same diameter and pour an inch or two of cement inside of them. This makes the tall structure much more stable. A couple of rocks placed inside could accomplish the same thing.

Once the frame is completed, the pump assembly can be finished and the screen bag should be constructed. Window screen material is inexpensive, plenty strong enough for this job and easy to sew on a standard machine. There must be enough material to enclose both ends. We make the bottom separate, sew it closed, pack the Bio material in and use a piece of loose parachute cord stitched into a fold at the end of the bag as the closure. This allows access to the pump if needed later.

The pump assembly consists of a submersible pump with a hose attached to it's outlet. The pump should be rated at the volume of the pond. i.e. a 300 gallon pond would use about a 300 gallon per hour pump. We add a piece of dowel rod as a stiffener and use stainless wire or parachute cord to wrap everything tight. Once the end of the bag is closed, it becomes hard to access the pump. The hose should be long enough to vent outside the finished cage or to reach a spitter or small waterfall.

The last assembly is the fabric bag. Don't design it too tight. A little loose makes the bag easier to remove for cleaning. Again, we place a piece of loose parachute cord into a sewn fold at the bag opening and use it as a drawstring to close the cloth bag around the hose/pump power cord. You now have a fully functional filter at very little cost. Lastly, add a tiny amount of Pond Magic to the pond to get the internal Bio Colony started.

If your pond is dirty now, it would behoove you to clean it as well as possible before placing the filter in it. Otherwise, it may take several bag cleanings before it removes all of the dirt in your pond. With a little occasional cleaning with a net to get out the large debris, soon your pond will be crystal clear and healthy.