Trying to put the basics about building a pond into one short article is very difficult, to say the least. However, in an effort to keep it concise, I’ve broken it down to 15 points that you should keep in mind when building a pond.
One of the first things to remember is that no two ponds are built the same way. Each pond is built on-site, and the terrain at every site is slightly different. Another thing to remember is that the builder of the pond has put his interpretation of what a pond should look like when finished. Some will place the rocks for a waterfall in one fashion, while another may place them a little differently. Others may use plant material around the rocks with a different treatment. However, one thing should always be the same, and that is following the basics of building a quality pond.
Before you even place your shovel to the ground, however, remember to call before you dig. You want to make sure you call the local water and power authorities to make certain that there are no pipes or power lines at the place you’re going to dig.
1- Select your location: Select the spot where the pond will go. Ideally, the pond should be in a location that can be seen from inside the house. That way, it can be enjoyed both indoors and out.
One thing you should keep in mind is not to build the pond where any runoff will run into or under it. Water under the liner can cause enough ground water pressure to push the liner, and the pond, right out of the hole. Also, you don’t know what chemicals the neighbor up the hill is using. You don’t want to find out the hard way, when it kills every living thing in the pond.
2- When building a Pond With a stream, you need to make sure that the pond is large enough. It has to be able to hold all the water that will run into it without overflowing whenever the pump or power is shut off. Otherwise, there won’t be enough water in the pond to run properly once the pump or power is turned back on, without refilling it first. Most skimmers today are supplied with overflow outlets. However, there’s only about a three- quarter-of-an-inch difference between optimum and overflow levels.
A 10- to 12-foot long, shallow, meandering stream easily holds 15 to 20 gallons of water. The longer, wider, and faster it flows, the more water will be “in suspension.” You should make sure you have enough surface area to handle it. This is especially critical when you have one pond flowing down into another.
Here’s a good rule of thumb: the surface area of the upper pond(s) and stream, plus the square footage of the surface area, must be equal to or less than the surface area or square footage of the lowest pond.
3- Size the Pumps and filters to the Pond size. First, determine the size of the pond or water garden. Then, calculate its gallon capacity. A 1,000-gallon pond should have, at minimum, a 1,200 gallons-per-hour (gph) pump. A 3,000 gph system would be more forgiving, though, and could handle more hiccups than the smaller pump. Make sure that the pipes can handle the flow of water that the system needs to work properly. A garden hose can’t give you much above 300 gallons per hour.
4- Leave slack in the liner at the attachment points. If you don’t, the silicone seals will pull loose from the settling of the soil and rocks. If you have a six- to eight-inch fold left over when you get to the top of the waterfall, just fold it over and cover it. If you leave a 10- to 12-inch fold at the base of your units, you’ll have extra liner if you ever have to do a swapout.
5- Don’t cut the liner until the pond, waterfall and stream are full and running. If you must cut it, leave at least one or two feet of extra liner. Just fold it over, roll it up tight and cover it with stones, dirt or mulch. You might need it later. If the dirt settles, or down the road you want to get a bigger pump, you’ll have enough liner to “stretch” and to handle any future leaks. (The inability to stretch accounts for more than half the liner leaks we professionals see.)
6- Make sure all equipment and pond sides are level. Water always sits at level, as it follows the path of least resistance. You’d swear at times that it was intelligent, the way it finds a low spot and leaks out. So don’t give it one—and if it does leak, you’ve got extra liner to pull up to fix it.
7- Ecological balance. A balanced pond has just the right amount of plants in it to consume the fish and plant wastes. If you overfeed the fish and don’t have enough plants, you will have green water 90 percent of the time.
Fish and plant wastes (ammonia) are converted by bacteria into nitrite. This, in turn, is converted by other bacteria into nitrate. Ammonia and nitrite, in small amounts, can be lethal to fish. Nitrates, however, can be concentrated at much higher levels without being harmful to fish. If there aren’t enough plants to handle the additional nitrate, nature will supply it in the form of algae. In a balanced pond, algae will still be present, but in low numbers. A mature, balanced pond will have no traces of ammonia or nitrites, only nitrates.
Go slow with a new pond. Don’t put in a whole bunch of fish or feed them a lot for the first month or so. Give the bacteria a chance to colonize in sufficient numbers to be able to handle the pond’s biological needs. This also lets the aquatic and marginal plants get established.
8- Check the structural integrity of the soil. Digging a straight-down, bathtub-shaped hole in unstable soil can cause major problems in the future. You don’t want to see a patio or wall collapsing into the pond. You might want to try stepping or shelving the hole to give the pond’s sides stability and depth. This will make the surface area slightly larger, but it’s worth it in the end. And did I say, “Call before you dig?”
9- Make the pond deep enough. Going deeper protects the fish in two ways. First, the water stays cooler in summer, and warmer in winter. They’ll be healthier, with better muscle tone and conformation.
Second, deeper water helps fish escape predators. Large, fish-eating birds, such as herons, can stand in water as deep as 24 inches, but they can’t catch fish while they’re swimming. Going slightly deeper in a fairly large area helps protect them from these natural-born fish killers. Raccoons catch fish in the shallows, but they don’t swim. Hawks and owls might snatch a quick fishburger on a fly-by, but fish learn quickly to stay low, except at feeding time.
10- Bigger is better. Larger ponds give fish more protection. And they’re easier to keep ecologically balanced. A larger pond allows the owner to explore more options without building a second pond. For instance, one water lily can overwhelm a 6'-by-6' pond, but a 15'-by-20' can comfortably have four or five, with room left over. Once folks get a pond, they’re always finding cool fish or plants they want to add. Going larger to begin with allows this flexibility from the start.
11- No chemicals needed. If you grasp the basics of design and eco-balance, you won’t need to play with chemicals.
12- Stay away from sh arp, pointy rocks. People like large, flat, slate flagstones because they cover a lot of area quickly, but they also cut liner, quickly and easily. Instead, use weathered and water-rounded rocks and gravels. Most stone centers have really nice, naturally weathered stones that don’t look like basketballs.
Any gravel placed in a pond should just cover the liner, not more than one-and-a-half to two inches deep. Again, make sure it’s rounded, without any sharp or broken pieces in it.
13- Size the liner. With a tape measure, find the maximum width and length. Add the maximum depth, twice (once for down, once for up). Then, add at least one extra foot to each side and end (two for width, two for length). You will now have enough liner to do your project.
Liner comes in five-foot increments of width; round up to the next size, never down. Since sand won’t stay on a vertical surface, always use an underlayment fabric under the liner; it’s cheap protection. You wouldn’t install new carpet without a pad, so don’t install your liner without underlayment.
14- Use the right size filter. Undersized filters are a common problem with ponds. The filter should be sized to handle the pump flow, not the gallons of pond capacity. You can use a 5,000 gph-rated filter with a 3,000 gph pump, but you can’t use a 2,000 gph-rated filter with a 3,000 gph pump and expect it to perform properly.
The more fish you have, the more filtration capacity you’re going to need to capture and convert their wastes to plant food. Choose a filter that’s easy to clean. Check with the supplier or manufacturer to see how often you should clean it; once a week or so should do it, if it’s properly sized. Oversizing the filter may cut down on the number of cleaning intervals, but won’t eliminate them.
Whatever you do, don’t undersize the filter. It’s going to cause more headaches than the small amount of money you’ll save is worth.
15- Always have some dechlorinator nearby. If the pond will be using municipal water, this product should be available any time more than five percent of new water is added to the pond. It should always be kept handy.
I hope you find this information valuable. I’ve shared my decades of experience installing ponds and water features with one goal in mind, and that’s your success.