Frequently Asked Questions on Planning and Constructing a Pond

Q. Where is the best place for me to put a pond?
Viewing from windows: Since most of us spend more time inside our homes than outside in our garden, it makes the most sense to locate the pond where you can see and enjoy it from the window(s) or room(s) you frequent most, such as your kitchen, sun room, family room or deck.
Orientation of waterfall: Be sure to orient your waterfall so that it is visible from the place you will enjoy it most.

Next to patio or deck: Having your pond next to your deck or patio is great – since these are areas for relaxation and entertainment. The sounds created by waterfalls and streams are soothing and can help eliminate traffic noises.

Flat ground and sloping ground are both fine: A pond does not need to be on flat ground. Take advantage of sloping terrain by adding interest with cascading waterfalls, streams and tiered landscaping.

Amount of sunlight: Five to six hours a day is ideal. Excess sun causes an overabundance of algae growth and green water. Conversely, shade trees drop leaves and blossoms into the pond, robbing the water of oxygen as they decompose. If possible, try for a happy medium.

Proximity to electricity and water:
Be sure your pond is close to a GFCI (Ground Fault Circuit Interrupter, an outlet) electrical source. Also, make sure your garden hose is long enough to reach your pond.

Desirable size and shape: Once you have decided on a location, you can design the size and shape of your pond. As a general rule, bigger is better. Make your pond at least 30 square feet with a minimum depth of 18 inches. Ponds this size will be more ecologically balanced, retain more stable temperatures, and provide greater movement for fish.

Geometrically shaped ponds with bricks or flat paving stones are a nice complement to formal gardens. For informal gardens, ponds can have a more natural, free-form shape bordered with stones of various sizes and shapes. Avoid tight curves or intricate shapes. These waste lining material, reduce water capacity and create stagnant areas where solid wastes can accumulate.

Q. How deep should I make my pond?

In most parts of the country, a pond for goldfish and plants of 18 inches - 24 inches is generally deep enough for fish to survive in the winter. For areas with very cold temperatures, such as upper New England or the upper Midwest, you should make your pond 30 inches or deeper so that it does not freeze completely to the bottom. Also, ponds intended specifically for Koi should be closer to three feet deep to allow room for these larger fish to swim freely.

Q. What type of liner should I use?

There are three basic methods to install a garden pond: concrete, pre-formed ponds and flexible liners. Liners come in weights ranging from tear-resistant, lightweight liners to heavy-duty EPDM liners.

Concrete Ponds: This option is not used often for residential ponds due to the cost in materials and labor and the eventual issue of cracking.

Pre-formed ponds: These are generally for smaller ponds ranging from 50 gallons up to 200 gallons. For in-ground applications, you simply excavate the shape of the pre-form and drop it in. An above ground installation takes a little more time and care when installing to ensure the pond form is stable and balanced. These are well-suited for both applications, although you cannot alter the shape.

Flexible Liner Ponds: These are constructed of 45ml EPDM and PVC. Check with the dealer to ensure the material is safe for fish. These materials are very popular for the following reasons:
  1. Less expensive per square foot
  2. Offers the most options in terms of creating the shape and size of your pond, stream or waterfall
  3. Easy to install. Unlike pre-formed ponds, flexible liners conform to any shape hole, and most come with a 20-25 year warranty.

Q. What size flexible liner do I need?

Here are two good rules of thumb to calculate liner size:
Liner length = Pond length + (2 x avg. depth) + 2 feet minimum overlap.
Liner width = Pond width + (2 x avg. depth) + 2 feet minimum overlap.
You don’t want to find out that the hole you spent hours digging is too large for your pond liner. It is very difficult to pack ground back into the pond to make the pond smaller. So dig the hole first, then measure for the liner.

Always buy a liner that is slightly bigger than you think you will need. You can use any excess liner to trim and place under streams and waterfalls that you’re building, or you can save it to use later. Note: The pond should be at least 30 square feet with a minimum depth of 18 inches.

Q. How do I protect my flexible liner from tears and punctures?

After the rough excavation phase, carefully remove all sharp objects from the surface, such as nails, twigs, rocks and protruding roots that could puncture the layer. Use a broom and dustpan to remove stones and debris.

Line the entire pond with one to three inches of sand and then properly position the underlying material to protect the main liner from root and rock punctures. Other underlining options include carpet padding and newspaper, but they won’t provide the same degree of protection. The underliner is crucial – even if the soil appears free of sharp objects, they can work their way to the surface as the soil settles.

Q. How do I install a liner?

Unfold the liner on the lawn or another flat surface nearby. With at least one person on each side of the liner (more for a larger liner), pick it up and walk to slide it over the hole that has been dug for your pond. Let the liner drop into the pond, making sure it extends evenly, well beyond the perimeter. Minimize the number of small folds by pulling or tucking them into the large folds. Hold the liner in place with bricks or rocks and fill the pond with water, causing the liner to conform to the pond’s shape.

Q. How to I hide the liner around the borders?

For a natural water garden pond, build a rock border around the edges, allowing rocks to overhang the water by one or two inches. To prevent the liner from showing, make sure the water meets the rock edging. During the excavation phase, a shallow shelf should be carved around the periphery of the pond as an area for placing your rock edging. When the pond is filled, the rocks around the edge of the pond will be partially covered by water, hiding the liner.

Extend the liner up behind the edging (rocks) and back fill with soil or rocks to create a barrier “dam” that securely holds the liner upright and prevents both drainage from the pond and garden runoff into the pond. Only after the pond is completely filled and the rock edging is in place should you trim any excess liner.

Q. Should I put rocks or gravel at the bottom of the pond?

We recommend that you do not put rocks and gravel on the bottom of the pond, but since there are many people who recommend it, we would like to present the pros and cons so you can make an informed decision.

Pros of having rocks and gravel on pond bottom:
  • Makes the bottom of the pond look natural and hides the liner material.
  • Creates biological environment for beneficial bacteria to break down organic sludge.
  • Rocks and gravel provide media for aquatic plants to attach their roots.

Cons of having rocks and gravel on pond bottom:
  • Sludge and leaves can build up in the rocks over time and the build up is extremely difficult to remove. A pond bottom free of stone can be easily cleaned of sludge by using a skimming net or pond vacuum.
  • There is plenty of surface area in the pond, waterfall and filter for beneficial bacteria – thus making the gravel at the pond bottom unnecessary.
  • It is difficult to control aquatic plant growth. Certain pond plants can prolifically spread out on the pond bottom, anchoring their roots to the gravel.
  • String algae can adhere to the gravel bottom and become difficult to physically remove.
  • Filling your pond with rocks adds cost.
  • Colorful pond fish don’t stand out as well as they do in a black-bottom pond.

Q. Can I join flexible liners together?

Yes. Your dealer can help you with the proper seaming tape for the liner. The liner needs to be very clean for proper adhesion. Be sure to follow instructions carefully.

Caution: It is best to avoid underwater seams. If possible, buy a liner that is large enough for your pond so you can avoid seaming liners together.

Q. How do I lay out and excavate a pond?
Layout: Use a heavy garden hose or rope to outline the pond’s edges. Place short stakes at one-foot intervals to retain the desired shape, and then make any final adjustments before digging.

Excavation: To excavate the pond area, start digging in the middle and work outward to avoid breaking the pond’s edges. You can create two or three tiers (shelves) in the pond – the top tier for edging and shallow plants, the others for taller marginal plants. Depending on the climate, shallow shelves should be between four and 12 inches. Mid-level shelves should be between 12 inches and 18 inches, and the deepest part of the pond a minimum of 18 inches. Be sure to check the depth and the layout plan regularly to avoid any unnecessary digging. To keep the surface of the pond level, stake out strings lengthwise and width wise using a line level.

Q. How do I estimate the gallon volume of my pond?

Your pond’s volume is important to know when sizing filters, pumps and UV clarifiers. It is also very important to know for proper dosing of water treatments. There are two different ways to estimate the gallon volume of your pond:

Graph method:
  1. Measure the length and width of your pond and sketch the approximate shape on the grid. Each square within the shape represents 1 square foot of pond surface area.
  2. Measure the shallow part(s) of your pond and the deep part of your pond. Record results in feet. Ex. 6 inches = 0.5 feet 18 inches = 1.5 feet.
  3. Shade the squares that represent the shallow part of your pond. Count the squares within the shallow areas. Multiply this number by the average depth of this section. This gives you the cubic feet of the shallow area.
        •  #Squares x average depth = Cubic feet of shallow area
  4. Do the same for the deep section of the pond to calculate the cubic feet of this area.
        •  #Squares x average depth = Cubic feet of deep area
  5. Add the cubic feet of shallow section and deep section together for total cubic feet of water.
        •  Cubic feet shallow + cubic feet deep = Total cubic feet
  6. Multiply the total cubic feet of pond water by 7.5. This will give you total gallons.
        • Total cubic feet x 7.5 = Total gallons

Simpler Method: This method takes less time than the graph method, but may not be as accurate.
  • Measure pond length, width and average depth.
  • Pond length x Pond width x Average depth = Cubic Feet
  • Cubic Feet x 7.5 = Pond gallons

Q. Why should I have a fountain, stream or waterfall?
As a rule of thumb, a minimum of 50 percent of your pond volume should be circulated in one hour. The more circulation, the healthier your pond will be.

Fountains, waterfalls or streams are excellent ways to achieve this circulation in an aesthetically pleasing way. Another option is decorative statuary that shoots a stream of water back into the pond (also known as “spitters”).

These water features also add much-needed oxygen to the pond.

Waterfalls and streams provide surface area for beneficial bacteria to colonize and help convert harmful ammonia into relatively harmless nitrates.

Choose the water features that suit your personal taste. You could use diverter valves to run fountains and waterfalls off the same pump, or use additional pumps.

Q. How do I add a waterfall?
Detailed illustrated advice on adding waterfalls can be found in the “Pond Construction” section of this website.

Be sure to position your pond liner under the waterfall stones in such a way that all the water flows back into the pond. Otherwise you will lose water from your pond.

Q. How can I expand the size of my pond?
There are several ways this can be done.

1. Replace liner
  • Drain pond (find alternative pond or tubs to temporarily keep your fish)
  • Remove rocks
  • Pull out liner and underliner
  • Expand width and depth of pond
  • Install new, larger liner
  • Use old liner for putting under waterfall or stream or use for a smaller pond

2. Expand your liner (seaming)
You can attach additional liner to existing liner using seaming tape. Note: It is very difficult to seam liner together while one is already in the hole. In order to get a good seal, the liner must be very clean and laid out flat. The best way to seam liners together is to remove the liner from the hole, clean the seaming area thoroughly and lay flat to apply the seaming tape. For best results use method 1 (replace liner).

3. Add another pond
  • You can add another pond next to your existing pond.
  • Adding a new pond may be easier and more interesting than expanding an existing one.
  • To ensure stability, make sure the distance between the bottoms of the two ponds is at least twice the depth of the deepest pond.
  • If the ponds can be built at different heights, then they can be joined by waterfall and/or streams and use the same pump, filter system and UV clarifier, as long as they are rated to handle the added volume of water. Connecting the ponds with a stream also gives you the opportunity to add a bridge across the stream, adding to the overall aesthetics.

Q. What are good plants for landscaping around the pond?
There are many good choices for plantings around your pond. Here are some helpful tips:
  1. Plant evergreens: These plants will give color and life to your pond year-round and especially during the winter months. Some examples: Hemlock trees, Japonica bushes, Rhododendrons, Azaleas and Ivy.
  2. Backdrops: Consider taller plants, tall grasses, shrubs and trees behind the pond to offer an attractive backdrop.
  3. Visibility of pond: Be sure to place tall growing plants so that they will not obstruct your view of your pond. 
  4. Rocky areas: It may be difficult to dig holes for small plants around waterfalls and streams because of the rocks and liner. Solution: Use TetrePond AquaPlanters – fabric planting bags that can be filled with soil and inserted between rocks. Consider placing ferns around waterfalls and streams to create a woodland setting. Small, creeping, succulent plants and moss can be placed in small rock crevices to create a natural look. If you are lucky enough to have large rocks or boulders in the area, work them into the design of your pond.

Q. How do I attach liner to concrete or rocks?

First ask yourself, “Do I really want to permanently attach rocks to the liner?” While formal ponds are often made with stone and mortar, many people make beautiful, natural looking ponds with stable rock borders without using mortar.

Should you choose to permanently secure rocks around the edge of your pond, here’s how to do it: Spread a thin layer of mortar around the edge of the liner and embed flat stones into the mortar. Mortar may also be placed between the stones.

Tips and Considerations:
  • When you mortar stones onto the liner, making any changes becomes a major project. Before mortaring the stone, be sure you are completely satisfied with your pond.
  • Consider enjoying your pond for a few weeks without the mortar, before setting the stones permanently into mortar.
  • Runoff from the mortar can be damaging to the pond fish. (Be sure the mortar is cured and the pond is thoroughly drained and cleaned before adding water and eventually fish).

Q. What if my pond overflows?

Your pond will overflow at some point, due to overfilling or excessive rainfall. When constructing a pond, build it in such a way that the “low spot” on the perimeter is where you want the pond to overflow.

Example: If a pond is built next to a house, be sure the “low spot” drains the water away from the house foundation.

Q. How do I plumb a pond for drainage and filtration?

  • Excavate your pond with a slight downward slope, 30 degrees maximum, toward its center or lowest point in the pond’s base where the drain will be installed.
  • Dig a trench in the pond bottom for a PVC pipe that will connect to the pond drain and exit just beyond the outside edge of the pond. Slope the trench downward so water drains away from pond.
  • Install the bottom part of the drain to the bottom of the pond according to instructions.
  • Connect the outside end of the PVC pipe to your external pump, then to your filters and finally to your water fall and pond – or you can add an external filter and then pump the water via a submersible pump in the filter to the waterfall.
  • Install necessary check valves to prevent water back-siphoning in case of a power outage. If the drain is to be used for water changes, install a valve only on the outside end of the PVC pipe and open it only for water changes.
  • Having a bottom drain makes cleaning your pond much easier. Incorporate it into your design at the beginning of pond construction. You’ll thank yourself later.
  • If the pond is already constructed, a vacuum drain may be placed at the lowest section of the pond. Attach a PVC pipe to the top of the drain and to the side of the pond. Route the tubing or PVC up the side of the pond to an external pump. Be sure to install a check valve so that the pump does not lose prime if electricity is interrupted.
TetraPond In-Pond Skimmer skims debris before it sinks.
TetraPond submersible pond light set – Create dramatic lighting effects.
TetraPond BioFilters for optimal pond biofiltration.