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Frozen Fish and How To Avoid Them This Winter
By Frank Greco, Senior Aquarist, New York Aquarium

After an extended mild autumn, the cold weather is finally here. Can snow and ice and, with them, the danger of power outages, be far behind? When winter is upon you, it's a good idea to make plans for maintaining your aquarium during a power or heat outage. Even a short power outage can lead to disaster and loss of animals if you are not prepared.

The first thing to do in an outage is to unplug your filters. If the power is off for a long time, toxins such as hydrogen sulfide and ammonia build up in the filter. When the power comes back on, the filter will spew this toxic cocktail back into your tank, perhaps killing the fish. Once power is restored, clean out all filters before using them.

Preserving biological filtration is another matter. If you use rotating biowheels, remove them from the unit and submerge them in the tank proper. For fluidized bed filters, remove as much water as possible from the unit, leaving the sand covered by only 1/4" to 1/2". For trickle filters, you can pour water through them once an hour or so or wrap them in plastic film in order to maintain humidity. Hooking any of these filters up to a 12-volt bait pump (small bilge pumps) will ensure their continued operation.

beluga whale
Like A Fish Out Of Water - Except in this case they're Beluga whales (Natasha, Marina and Maris) are carefully lifted from their tanks in November to head South for the winter. They're on "breeding loan" at the brand new Georgia Aquarium. Last we heard the New York Girls and the Southern boys were getting along swimmingly. Talk about long-distance romance!

During a cold-weather heat or power failure, maintain your tank's water temperature as best you can. Since glass is a poor insulator, heat loss can be rapid as the house temperature drops. The easiest way to prevent heat loss is to wrap the tank in Styrofoam or some type of insulating blanket (the thermal type, such as are used to insulate water heaters). Styrofoam can be purchased in sheets and cut to fit the size of the tank. Make sure it is a tight fit, and use duct tape to fasten the pieces together. Do not forget to insulate the bottom of the tank (if it is exposed) and the top. Punch a few small holes in the top for the air lines. If you use an insulating blanket, wrap it around the tank, using duct tape to keep it in place. While neither of these methods will entirely prevent heat loss, it will slow it down. Never heat tank water on the stove and pour it back into the tank! Such wide temperature swings will virtually ensure that your fish will come down with a parasitic infestation. Better to allow the temperature to slowly drop, since your fish will adjust to it--to a point--better than they would such a temperature change seesaw caused by pouring heated water in the tank.

Once you've figured out a way to keep your tank water warm, work on aeration and filtration. The simplest way to aerate is to remove buckets (or cups, if it's a small tank) of tank water and pouring them back into the tank from a height of 6 inches. Do this at least once an hour, more if the animals seem to need it. Another simple method involves hooking an air stone to a bicycle pump and pumping air into the tank as above. The addition of 1 cc of 3% hydrogen peroxide per 10 gallons once an hour can also be used, but this is good only for short power outages since the addition of too much peroxide will destroy the biological filter. The hydrogen peroxide method should be used only as a last resort.

Python Products

Battery-powered air pumps are the best way to aerate/filter your tank during a power outage, no matter what the temperature is outside. There are two types available to the hobbyist, one of which works on "D" batteries while the other works on a 12-volt car or boat battery. Either will work, but the life of the "D" cell pump is short and you will have to replace batteries often. The 12-volt pump is better. Hook your air pump to an air stone or box filter containing carbon and zeolite, or, better yet, a biologically-active sponge filter and box filter combo. A 12-volt bait pump (bilge pump) may also be used to aerate/filter the tank, but they use more power than most 12-volt air pumps. The air lines should be run through the cover.

Unless you know the power will be off for a long time, do not feed the fish. Most fish can survive three to five days without being fed. If you must feed them, whether for the health of your animal or your own peace of mind, do so sparingly. Remember, your tank's life support system has been compromised, and adding more organics like fish food will hasten water degradation.

If you follow my advice, your aquatic charges should make it through the power outage with little or no problems. Once the outage is over, do a 25% water change (remember to use your gravel cleaning siphon) and replace the carbon or whatever chemical filtrants you are using. Watch for signs of disease (mostly Ich, which looks like white spots) and treat as necessary.

Frank M. Greco is a long-time hobbyist and Senior Aquarist at the New York Aquarium. Visit him on the Web at Fishy business going on in your tank? Write to Frank and he may answer your question in his next column!

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Most recent update: 2/19/06
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