Q. I want to install a fish pond this spring. After doing a lot of reading and thinking I decided to use a pond liner rather than cement or fiberglass. I thought everything would be fairly simple at that point, but when I went to investigate pond liners I discovered a large selection of materials and a wide range of prices.

How should I choose which liner to use? Our winters are cold, the ground heaves when it freezes and the soil is very rocky. We also have many tree roots throughout the soil.

I want to make the pond about 26 feet long and 14 feet wide in a kidney shape. How do I determine the correct liner size?

A. Let's start with the liner sizing. The basic rule simple. To determine the liner's length measure the longest distance across the pond (that is its maximum length). Add to this twice the maximum pond depth. Then add another 2 feet. For the liner width measure the maximum width of the pond, add twice the depth, and then add another 2 feet.

You didn't indicate the pond depth you are considering. I suggest you think in terms of 2 feet on average, with a 4-foot deep section and a 1-foot shallow area. In your case the liner should be 36 feet by 24 feet, for a total of 864 square feet.

You will almost certainly have excess liner material when the pond is finished. Depending on its dimensions you may have enough excess to construct a waterfall or small stream. You should save several 1-foot-square pieces for patching, should the liner get punctured.

It used to be that if you wanted to install a pond liner you had three options: 1) create a temporary pond using a 3-mil painter's plastic drop cloth (it would barely last a summer), 2) use a swimming pool liner, treated with heavy baths in potassium permanganate and then let sit for a year without fish (to remove toxic chemicals), or 3) use a 20-mil PVC liner.

Today, the range of fish-grade pond liners is large and growing, and both their quality and price are rising. Still, there are significant differences worth considering.

One popular pond liner is the classic PVC liner, which is sold in various thicknesses. For example, some pond suppliers offer 20 mil and 32 mil PVC liners. Thicker liners tend to handle outdoor wear and tear better, and this is reflected in the "warranties" that come with them. Tetra offers 10 years for its 32 mil PVC liners. (Understandably, such warranties are very specific. If your golden retriever jumps in the pond and puts a claw through the liner, it's your problem.)

In very cold climates PVC liners get stiff and brittle. Some will crack under stress and are more easily punctured or torn by tree roots and rocks in the subsoil. PVC liners are also UV sensitive, so it's important to properly cover the material with water, stone, wood, etc. Nevertheless, these are relatively inexpensive liners and can be found in many basic sizes in local aquarium stores. This means they are ideal for weekend projects. Add to this the fact that most first ponds are remodeled within the first few years of construction, and I believe that PVC liners are the best choice for new pondkeepers.

EPDM is another liner material. It is a thicker (45 to 60 mil), more rugged material. EPDM is heavy and therefore also a bit more difficult to work with. These liners have better cold weather properties and UV resistance. Twenty-year warranties are common.

If you decide on EPDM be sure that you buy certified fish-safe liners. Some EPDM marketed for roofing work is toxic to aquatic organisms, so do not just drop into the local building supply house for a liner. Fish-safe EPDM liners are available from most pond retailers and mail order pond firms.

A third option is a multi-layered plastic material. These are lightweight, yet very rugged. They hold up well in cold. I have noticed they tend to tear more easily than EPDM if a coarse surface (such as a stone) scrapes along the liner. The primary source for these liners is Reef Industries (713-507-4200) in Houston, Texas.

Selecting a liner requires some thought. Better quality is not necessarily always the best choice. For example, a thicker, more durable liner isn't always preferable. Thicker liners cost more — sometimes a lot more. If this is your first pond I can almost guarantee that after a year or so you will want to make it bigger, change its shape and orientation, or link it to a stream or second pond. Paying twice as much for a liner with a 20-year lifetime may not make sense if you rip up your pond every three years. Less expensive liners are the intelligent choice here.

If you are doing the project on your own, a light, easy to maneuver liner is important. If so, multi-layer plastic liners fold and sculpt well. These are also among the least expensive of the liners on the market. Conversely, a long-established pond in need of a new liner might be best served by a very high-quality EPDM liner with excellent durability and longevity.

What is very clear to me is that pond building has never offered more or better choices in construction materials. This is good news for novice pondkeepers and old hands in the pond hobby.

In a Barrel
Q. I have three lovely ranchus living in a 15-gallon aquarium. They have gotten large, but have lost a lot of their color. I would like to put them outside in a larger amount of water, but am not really ready to build a pond.

A local nursery has plastic half- barrels that they are selling for container water gardening. They hold around 30 gallons. Would these be safe for keeping our goldfish outdoors? Would I need a filter?

A. I haven't really said much about container water gardens in this column over the years, which is a unfortunate because they are a very versatile alternative to aquariums and ornamental garden ponds.

Container water gardens are usually between 20 and 150 gallons, although I have seen smaller and larger examples. Like an aquarium, they can be set up in an afternoon without any of the laborious digging a pond requires.

Besides the many commercial products available I have seen container water gardens that used converted horse troughs, old claw-footed bathtubs, half whiskey barrels and wash tubs. Anything that can be made to hold water can become a container water garden. Just make sure the container has been cleaned thoroughly to remove potentially toxic chemicals.

The simplest setup excludes fish entirely. Put the container in a sunny location, place soil (or pots) on the bottom and fill with water. Presto! A water garden lives. There are many flowering wetlands plants to choose from, and even some water lilies that thrive in these containers.

Of course, this standing water source becomes an attractive breeding ground for mosquitoes. That usually leads folks to add a few goldfish. Problem is goldfish do not really do a good job eating mosquito larvae, especially if the fish are well fed with fish food. In warm climates — and especially during the summer — tropical fish do amazingly well in container water gardens. And some are voracious mosquito eaters.

A container water garden can be a fine home for your ranchus if you take a few precautions. First, I would not keep the container in a location that gets more than an hour or two of direct morning or late afternoon sunlight because the water can get very hot. Find a location that shades the container from 11 a.m. to 3 p.m.

Second, fish in a container water garden are easy pickings for cats and raccoons. There is really not much you can do about this, but it is a consideration in designing and placing the water garden.

Third, whether or not you need a filter will depend on many specifics. Soil and gravel on the container floor should provide more than enough space for nitrifying bacteria. One or two fish in a 30-gallon container with a gravel floor and good plantings should be fine without a biological filter.

Proper aeration may be a problem. Sometimes a simple bubbler can keep dissolved oxygen levels high (and CO₂ levels low). Or a small pump may be needed to maintain circulation. (Circulation also has the added benefit of discouraging mosquito breeding; they prefer still water.) However, too much turbulence in a container water garden can inhibit plant growth (especially water lilies) and stress the fish. The flow rate should be one-half to one container volume per hour.

Lastly, do not overfeed! Polluting the water with food and fish waste will lead to very rapid water quality degradation. The container water garden is more like a fish tank than a pond in terms of its ability to forgive overfeeding mistakes.