Q. I have recently found out about your magazine. I assumed that it would have nothing I would be interested in as we mainly have an outdoor pond, not an aquarium. But, now that I know there is a regular feature on ponds, I sent in a card today to start my subscription.

I have found your advice on overwintering pond fish interesting and helpful, but much of the information seems directed toward those who live where winters are not as long and cold as they are in the most northern areas of the country. We are having problems here keeping our fish from dying every spring. We don't lose them all, but the past two years have been particularly bad. We lost 140 fish last spring, mostly the previous summer's babies, as well as some of the bigger ones. We realize that we will lose some because of overpopulation, but we really hate to lose so many.

We keep trying to come up with new ideas on how to keep the pond covered to prevent the ice from going so deep. We have a 3-foot deep artificial pond with a liner. It is oddly shaped, somewhat like a fish, about 18 feet at the widest point and 100 feet long. We stock comets, shubunkins and fantails. Can you help us?

A. Welcome to AFI. The "Ponds & Pond Fish" column has been a part of AFI from the very first issue, thanks to the great foresight of our editor, who realized that pondkeeping was not just aquarium keeping without a roof.

I make every effort to discuss things that are "unique" to pondkeeping — like winterizing. But, let me encourage you to read all the sections of the magazine. You will be surprised how many important pondkeeping problems are addressed by the other columnists who write about catfish, saltwater fish and so on. I always learn new things from them (which I steal and rewrite here months later).

You are right, the last two years in New England have been especially bad. Last year was the first year in over a decade that I lost any goldfish to winter kill. About half of my very hardy comets died. This past winter the ice was extraordinarily thick compared to the last 10 years, but in fact it was probably closer to what we should expect as normal — so we had better get used to it.

Your pond probably holds between 15,000 and 20,000 gallons — fairly large by ornamental pond standards. A 3-foot pond depth, however, is simply not adequate for our area. You will always lose fish — perhaps the majority. You will need to dig down to a depth of at least 6 feet before you can expect a better survival rate. After all, the frost line in your area extends over 5 feet deep!

If you cannot go deeper, then you might try to maintain a large permanent opening in the ice. This is not as easy as it sounds in our area (or the northern midwest and plains states). Simply covering the pond with plastic or hay, as suggested in some books and magazines, will not work in the northern U.S.

Recently, there has been a lot of discussion about heating ponds in winter — the idea is a British import. Unless you are incredibly wealthy, however, I suggest you forget it. Our climate is far colder and our winters much longer than those in Britain. And, frankly, I think heating ponds in winter is an inexcusable waste of energy.

The other possible remedy is a cluster of thermostatically controlled de-icers. These float on the pond surface and keep a small hole open that allows water and air to make contact. They come in 1000- and 1500-watt sizes, but you would not want anything under 1500 watts. Even then I am not sure that a de-icer will do much good in your area. Depending on a number of things peculiar to your site, the ice might freeze below the heating element, leaving you with an ice bowl of warm water — and dead fish.

Because these heaters cost under $50, buying two or three will not set you back much. It might be worth experimenting. Keep in mind that operating costs might run $50 or more per de-icer per month. With three, your winter electric bill could jump a hefty $600 or more.

So, you might want to consider a different approach: building a sheltered (indoor) holding tank for your best specimens and breeders. As my regular readers know, I bring all my koi indoors every October and winter them in a 1300-gallon holding tank in the basement. It is worth the trouble. I have never lost one this way. Conversely, I have never had a single koi survive over winter outdoors.

A 1000-gallon tank, kept at about 50 degrees Fahrenheit all winter, only requires 67 square feet if it is designed to hold 2 feet of water. That is a little more than an 8-foot by 8-foot square. You should be able to safely hold 100 or so goldfish at that temperature, assuming good biological filtration and sparse feeding. If water temperatures rise close to 60 degrees Fahrenheit, you will not be able to keep this many animals in the holding tank.

The biological filter should be external to the tank and should be fully active before the fish enter the holding tank. On the one hand, if you have an active outdoor biofilter with lightweight media, you can just transport it to the basement. (I move 15 to 20 cubic feet of biologically active bioballs to the basement before I begin moving the fish. I would never attempt that with gravel media.)

On the other hand, you could set up a separate biological filter with its own media and then feed it ammonia for a month or two before moving the fish. Ordinary household ammonia (no detergents, additives, etc.) is the same ammonia that fish excrete. The source of the molecule that binds nitrogen to several hydrogen atoms is irrelevant. Therefore, if you start feeding a new biofilter ammonia every day, nitrifying bacteria will begin to feast.

Fill the holding tank and filter box with water. Your circulating system should move a complete volume of tank water at least once every two hours, and preferably once an hour. You should have some mechanism for good aeration: venturi jets, cascades, trickle columns, etc. Then add enough ammonia each day to get readings of 3 parts per million (ppm). After several weeks you will find measurable nitrite in the water, and several weeks later nitrate. Once ammonia and nitrite readings go to zero, despite the fact you are still adding ammonia, it is safe to add the fish.

To keep the fish from getting stressed from the move you should empty the holding tank completely just before the move begins and refill it with pond water from outside. In this way the fish will be going from the pond to the tank with no change in water quality. Over the next few weeks you can do partial water changes. When spring comes and pond water temperatures move into the mid-50s you can return your fish outdoors.

Gravel Plants
Q. In the May 1994 issue of AFI you asked for information on plants that have been grown successfully in basic gravel substrate. Here are my results: pickerel rush (Pontederia cordata), floating heart (Nymphoides peltata), umbrella palm (Cyperus alternifolius) and water arum (Peltandra virginica). All plants are bare root in pots.

None has ever been fertilized. The pickerel rush and the floating heart flower profusely and reproduce heavily. The palm reproduces heavily and gets a few giant flowers (this plant is wintered indoors).

My pond is 9 feet long, 6 feet wide and 18 inches deep. It is a hard-shell, one-piece unit. My pump circulates about 160 gallons per hour. From May until mid October it is submersed in a 5-gallon bucket in the pond and filled about three-quarters full with lava rock. This is cleaned about every eight weeks. I leave the pump running in the winter and no solid freeze has occurred. I drop the plants to the pond floor in winter.

Last winter I decided to take the fish — four 8-inch koi and three 5-inch goldfish — indoors for the first time, because I had a feeling it would be a tough winter. I kept them in a 90- and 110-gallon tank.

I really enjoy your column. I used to think of goldfish as feeders only, but they are now my favorites. They don't have territories — big and small get along. They are hardy and long lived, many are inexpensive, and they have some of the most phenomenal colors and patterns in the fish world.

A. Thanks for your fascinating letter (I could only reprint a small portion). The information you provide on pond plants will be of great benefit to the other readers. I estimate that your pond holds about 400 gallons.

I want to highlight your simple but effective pond filter system: a biofilter made from a 5-gallon bucket with lava rock and a submersible pump and a vegetative filter composed of bare-root plants in pots. This is an excellent model for anyone contemplating their first pond (as well as those who are having problems with existing ponds). Sounds like you have everything well in hand.