## Creating a homemade pond water filter is simple and easy.

Oxygen is probably the most important element to a healthy water environment, with the exception of the water itself. The fish require oxygen. Another organism vital to a healthy fishpond is bacteria. They will literally eat and thrive on the wastes and nitrates a healthy fishpond produces.

In the construction of a homemade pond water filter, you are not filtering the water. In reality, you are treating the water with a natural bacterium that consumes the nitrates from the fish waste. This bacteria thrives in a habitat of small nooks and crannies. It also relishes fast moving water filled with nitrates and oxygen. The same type of water environment is found in flowing streams with a gravel bottom.

Let us examine the data you will need for your homemade pond water filter.

First, what is the size of your pond? This should be calculated in square feet. A rectangular pond is simple. The area is an easy calculation of multiplying the length times the width.

A circle is just as easy. Take the total distance across, called the diameter and divide that by two. Let us say we have a ten-foot diameter pool or 10 feet across the pond. The radius would be five feet. Next, square the radius which is five, 5 x 5 = 25. Now all we have left to do is multiply by Pi. We can simplify the number to 3.14 since this is not too critical. The resultant formula is 25 x 3.14 = 78.5 square feet. The actual formula for area is, Area = 3.1416 x Radius^2 (^2 = squared).

Now that we have the area of the pond at 78.5 square feet, we can now calculate the area of the filter material. We can also figure how much water we need to pass through this filter in one hour.

Our imaginary pond is on the average four feet deep. We multiply 78.5 square feet x 4 feet = 314 cubic feet of water. Water has a capacity of 7.48 gallons per cubic foot. Round up to 7.5 gallons. Total capacity of our fishpond is 314 cubic feet x 7.5 gallons/cubic foot = 2355 gallons.

A good rule of thumb for any pond filter system is to pass at least half the total volume of water through your filter system every hour. We will need a pump that can push 2355 gallons x .5 hour = 1177.5 gallons. Round this up to approximately 1200 gallons per hour. It is always better to calculate a little more water flow than too little.

Now, with these two important numbers on paper we can proceed to calculate the size of the filter our pond will need.

The surface area is 78.5 square feet with a pump hour capacity of roughly 1200 gallons per hour. The filter system should have a surface area of about one third the area of the pond. In our case this would be, 78.5 square feet/3 = 21.2 square feet. This is a large sized filter, especially if we take this as the total surface area.

The bacterium prefers to live in small nooks and crannies. This is where lava rock or any other porous material comes into play. Materials with lots of small holes (such as lava rocks) are a perfect fit for these bacteria to thrive in. The lava rock has a vast surface area due to all of those tiny holes. The action of the water flowing over these rocks provides abundant oxygen for the bacteria to grow and devour the fish waste.

The filter surface area from our imaginary fishpond is 21.2 square feet, or approximately, an area a little larger than four foot by five feet. If you were to take the small lava rocks and spread them evenly on the ground, one layer deep in a four-foot by five-foot square. This would be your surface area of the filter.

A large plastic 30-gallon trashcan is a perfect receptacle for the filter material. The volume of this container will fit for our recommended filter area. Scoop those rocks up and place them in the 30-gallon plastic trashcan. You will notice that they fit with room to spare. In fact the more lava rocks you add, the greater the filter area.

The above calculations were the difficult part, now the fun begins. The plastic container is paintable and you may match the colors to fit any background. Alternatively, you may choose to hide the filter by stacking landscaping rocks around it.

The method described below is for a gravity flow system. This method works well for creating a nice waterfall that greatly enhances the oxygen content to the fish.

1. Drill 12 holes in the container. The holes should be facing the pond side with a 3 x 4 pattern, three holes high with four holes across. The hole spacing is approximately five-inches on center. The holes should be no less than one and one half inches in diameter. The lower row of holes should be six inches from the bottom of the container. This is important if your pump fails, as the bacteria will die after five to six hours from lack of water and oxygen. This small water reserve will give the bacteria a chance of survival if your pump fails.

2. Line the inside of the container, covering over the exposed drilled holes, with one-quarter inch screen mesh. An 18-inch by 18-inch square piece will fit nicely. This will keep the lava rocks from falling out of the holes.

3. Move the filter to the pond edge. Under the container, install a heavy-duty plastic sheet, six mil or greater in thickness, and drape it into the water. You can trim the excess later. You should elevate the filter container a few inches so a greater waterfall effect is achieved. You may contour the gravity flow by using the plastic sheet. Form any soil and rocks so the water will flow into the pond. Make sure the container is level and properly seated.

4. Carefully add the lava rocks. Take care not to disturb the mesh screen--it needs to remain in front of the drilled holes.

5. Stack the remaining rocks around your filter for stability and the proper effect for a natural background.

6. Attach the outlet pipe from your pump into the container. This can be done any number of ways. One method is to loop the hose under the handle of the plastic trashcan. You may secure the pump hose with a couple of plastic wire ties to the handle. Be sure that the end of the hose is under approximately six inches of the lava rocks to keep it from spraying about.

This filter design should last the entire season. No cleaning is required as the constant flow of water and oxygen should keep the bacteria growing and healthy.

Seasonal winter removal of the filter is important, as freezing water will damage the plastic container. Allow the rocks to dry thoroughly before storing them for winter. Constant freezing and thawing, if water remains in the porous rock, will deteriorate the lava rocks.