Estimate the volume of water in your pond by first determining the surface area of your pond. Measure the pond's length and width using measuring tape and draw a map of the pond in scale onto a piece of graph paper. Draw your map using feet as the scale measurements with each square representing a set number of feet across; for example, one graph square equal to 10 feet of measured pond surface. Count the number of squares that the pond fills, rounding off partial squares by adding one to the count for a square containing majority water and not counting those not containing a majority of water. Use the scale for your drawing to determine the surface area by calculating the area of each square---by multiplying the width of the square by the length---and then multiplying the area by the number of squares.

Determine the average depth of your pond by measuring the depth in the center of each square mapped using a depth stick marked in meters. Add all the measurements and then divide the total by the number of squares.

Multiply the surface area by the average depth to get the volume of your pond. To get the water volume in gallons, multiply the volume by 6.7 for an oval pond, 5.9 for a circular pond or 7.5 for a rectangular pond.

Buy enough activated charcoal to treat a pond of your volume, about 1 lb. for every 1,000 gallons of water.

Place a pair of stockings into a second pair to create a double layer. Place the charcoal into the stockings and then tie the ends closed.

Tie a string around the stockings and plant a stake into the ground near a high-flow area of your pond, such as a waterfall. Attach one end of the string to the stake and then run the stocking containing the charcoal out into the high-flow area; the string and the force of the water will keep the charcoal afloat. The water will flow through the high-flow area while the charcoal collects the impurities, cleaning the water as it passes.

## Things You Will Need

- Measuring tape
- Graph paper
- Depth stick
- Activated charcoal
- Stockings
- String
- Metal stake
- Hammer

## Tips

- Replace the charcoal every six months.
- Increase the charcoal used by three times the amount if there are known contaminants in the pond such as detergent or pesticides, and replace monthly until the water clears.