Overcrowding a fish pond can cause all manner of trouble. An overabundance of fish can tax a pond's ability to provide biological filtration, leading to a buildup of toxic ammonia and nitrites. Additionally, too many fish can deplete a pond of oxygen. While these conditions harm fish, they also encourage the growth of unsightly algae. You must understand the capacity of your pond to in order to avoid these issues.
In many situations, you can save yourself a few steps on calculating your pond's capacity. Most stocking guidelines for stocking a pond hinge on the pond's volume or surface area. If you purchased a prefabricated pond, like those sold at hardware stores, either the store or the manufacturer usually has a record of the volume and surface area. And if a contractor builds your pond, he likely has detailed records regarding its volume and surface area. If you can get this information, you can save yourself considerable effort and time.
Calculating Surface Area
If you have to calculate the surface area of a pond, you will need a bit of geometry. First, figure out the nearest shape of your pond. For example, many ponds have a roughly circular shape, in which case you'll treat it as a circle. Keep in mind, that if your pond does not have an exactly geometric shape, err on the side of caution by underestimating the size rather than overestimating it. For roundish ponds, the formula of one-half the distance across the pond multiplied by 3.14 will give you the surface area. For rectangular ponds, multiplying the length by the width gives you the surface area.
Calculating the volume of a pond requires you to first find the surface area, then the average depth. To measure the average depth, measure the depth of the pond in at least three areas, including the shallowest and deepest parts of the pond, add then together and then divide by the number of points you measured. The more points you measure, the more accurate your calculations. Once you've measured the surface area and average depth, multiply the average depth by surface area.
Different experts have different guidelines for stocking ponds. One guideline holds that you need 300 square feet of surface area per koi, and half of that per goldfish. A different guideline holds that you need 30 gallons per fish for goldfish, and at least 150 gallons per koi. Keep in mind that all of these guidelines assume you have a well-maintained pond with plants and a filtration system. Keep in mind that pushing guidelines can result in an overcrowded pond, and all the problems that come with that.
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