Definite noticeable changes occur in koi and goldfish, plants and the pond itself as the temperature of the water begins to drop. Leaves on water plants start to brown and die back. Koi and goldfish become less active and require less food. Leaves fall and cover the surface of the pond. The pond may suddenly clear up after not being clear all year. These are changes we see. The changes we do not see are just as important. Nitrifying bacteria, present all spring and summer in the biofilter, stop reproducing and become none effective. Biological functions in the fish’s bodies, controlled by temperature of the water, slow down and eventually the fish hover at the bottom of the pond in a state of semi-hibernation.
Netting the Pond
Catching leaves is not the only reason to net the pond for the winter. Basically all water plants, including microscopic algae, die back in cold water. Once murky with green the pond suddenly becomes clear as a bell exposing our colorful koi and goldfish to the world above — mainly hawks, owls and blue herons. To make matters worse lily pads and other plant cover die back providing fewer places for fish to hide from these hungry predators. Blue herons and raccoons do not hibernate during winter. In fact, blue herons are more abundant in southern climates such as ours having migrated for the winter from Canada and other cold regions. Netting not only catches falling leaves it can help thwart a predator’s attempts at feeding from your stock. A fine but strong netting of 1/2” squares is available in a width of 14 feet and can be cut to the length required. Secure it around the perimeter of the pond by placing heavy objects over the edges or using ground stakes. Make sure when measuring for netting you allow extra on the sides to do this. Also, don’t forget to cover the waterfall or stream if your aim is to catch as many leaves as possible.
Fish tend to lose their feeling of security during the winter when the pond is clear of all plant life. Fish instinctively know that they are "easy pickins" for an opportunistic blue heron. You can provide hiding places and give peace of mind to your fish very inexpensively. Try doing one or more of the following:
Make a Trashcan Tunnel — Cut the end out of a large, round plastic trashcan. Then cut it lengthwise in half. Most trashcans will be equipped with a handle to use when placing and removing it. The tunnel will become your fish’s favorite hangout throughout the winter. Remove it when natural shelter has grown back.
Float Styrofoam — It won’t be attractive but it will put your fish at ease and offer shelter from the predators. Styrofoam lids are great to simply float on top of the pond.
Add Silk Water Lilies and Hyacinths — Silk water lilies and hyacinths last a long time and the bloom never dies. Lilies come in almost any color available on the real ones and you can get just the lily pads as well. Both the flower and the pads are available in different sizes. Hyacinths are available with purple and white blooms and with no bloom at all. The addition of these realistic silk plants to your pond adds color while offering some protection against predators.
Find Silk Water Lilies and Hyacinths at our online store.
Provide a PVC Playhouse — 4” to 6” PVC elbows and pieces provide excellent hiding places for koi and goldfish. They may be painted black to melt into the background of the liner.
Feeding the Fish
When water temperatures are consistently below 62º cut back on feeding. If you feed them twice a day - feed them only once. If you feed them 4 times a day - cut it back to twice. You will begin to notice the fish will want to eat less as the water temperature drops. Switch to a food high in wheat germ such as our own M-Wheat™. Occasionally substitute steamed rice (no salt or butter, please), cooked pasta or canned or frozen early peas. All these foods are low in protein and easily digested. This can also be fed to the fish in spring when the water is just heating up and the fish haven’t quite regained their immunity systems.
Find M-Wheat™ Seasonal Fish Food at our online store.
Stop feeding koi and goldfish anything at all when the water temperature is consistently 50º or lower. Some folks say that you can feed them wheat germ food as long as they will eat. We don’t agree with this for ponds in the Metro Atlanta Area. In warmer climates like ours it is unusual for water temperatures to remain under 50º for more than 10 or 12 weeks. This is the time when fish are virtually dormant and eating becomes more stressful to them than beneficial. Fish have no stomachs. If a fish eats in very cold water the food may not be digested and could lead to an internal bacterial infection known as Sepsis. Why, if the dormant time is so short, would we want to subject the fish to stress?
Fish Health Concerns
When water temperatures drop the immunity system of the fish is the first thing to go. Dangerous fish parasites, such as costia and flukes, can thrive in these not-yet-too-cold water temperatures and, left unchecked, fish become vulnerable to diseases brought on by these parasites due to lessened immunity. We recommend a salt treatment to be administered before cleaning the pond. Salt, in the correct amount, is a natural tonic for the fish. It encourages production of the fish’s natural slime coat that assists with protecting the fish from the elements. Salt also kills many of the common parasites that can kill fish.
To perform a salt treatment: Remove your plants and administer 0.3% (3 lbs. per 100 gals) of non-iodized, mineral-free salt. We carry pure salt in 50 lb. bags but ice-cream salt from the grocery store will do just fine. Make a 50% water change after 3 weeks and return the plants.
Koi and goldfish need a clean environment for the winter. Ponds that winter over full of leaves and debris become havens for parasites and anaerobic bacteria, such as aeromonas and pseudomonas, that are just waiting for the water to heat up to become health hazards for the fish. The build up of muck in the pond is responsible for producing hydrogen sulfide, a gas that smells like rotten eggs and is deadly to fish.
Once you know most the leaves have fallen clean the pond thoroughly. Remove any muck on the bottom and in the waterfall or stream. Do not scrub off the sides of the pond. The jelly-like substance that grows on the sides is beneficial. A blast from the garden hose will remove soil off the sides without disturbing the coating.
To Run or Not To Run the Pump
A question we get asked a lot is, "Do we shut off our pump and filter for the winter?". Before we answer that, let’s first examine how running the pump affects the pond during winter.
If the pond is designed correctly, the pump will pull water from the bottom of the pond. Water on the top of the pond freezes first. Water on the bottom, if left undisturbed, will remain warmer. Our fish need to stay in water temperatures above 36º. When the temperature is freezing it’s to our advantage not to run the pump and pull up the warmer water on the bottom of the pond and expose it to the freezing temperatures at the top.
It’s true that running water does not freeze as easily as still water and, unless expecting a hard freeze, it may be worth while to run the pump so the pond doesn’t freeze over. If you have a submersible pump you can do so without compromising the warmer water on the bottom by raising the pump to a higher position, perhaps onto a plant shelf or milk crate, thus re-circulating cooler water up top instead.
If water is being pulled through a bottom drain this cannot happen. The only way we would recommend keeping the pump running is by closing the intake of the bottom drain and allowing only the skimmer to take water off the top.
When water runs along a stream or through a waterfall it is exposed to freezing air temperatures and will cool off much faster than if it is returning directly to the pond. You can shorten the amount of time the water is exposed to the air by taking the waterfall out of the equation and returning the water line directly to the pond, perhaps by way of a temporary set up where a submersible pump is set up on a plant shelf.
Keep in mind that at some time during the winter you may not have a choice whether to run the pump or not. If the electricity goes out — so will your system! Use common sense. If a winter storm is approaching we would recommend that you shut the system down and take preventive measures (many of which are listed) to prevent any damage to expensive hardware.
If the fish are healthy it’s perfectly fine to turn off the pump when we experience freezing weather!
Fish are inactive and require less oxygen in cold water. Cold water retains dissolved oxygen better than warm. Plants do not live in cold water so at night they will not be consuming dissolved oxygen. It’s logical to say that when water temperatures are below 40° we can safely turn off the pump without fear that fish will be adversely affected due to low dissolved oxygen levels. Whether or not pond water is circulated through the biofilter is basically of no consequence since nitrifying bacteria is not active at these temperatures anyway.
Only strong, healthy fish can weather the winter. Occasionally people will experience fish loss due to fish being weak and immunity systems being low. Factors such as gill disease, parasites and bacterial infection play a part in the overall health of the fish and its ability to withstand the colder waters of winter. A fish weakened by disease and past gill damage will be the first to die when the system shuts down for the winter. The same is true for baby fish. Only healthy fingerlings will survive the winter.
If the Pond Freezes Over
Ponds freeze from the top and, especially in colder climates, may freeze into a solid piece of ice several inches to a foot deep. DO NOT CRACK OR BREAK THE ICE WITH A HAMMER. This will hurt your fish. Keep a whole in the ice with a de-icer unit. Be sure it has a heat guard to protect the liner.
Find Pond De-Icers at our online store.
Do not leave the pond completely iced over for more than a week. Toxic gases accumulate under the ice and must be allowed to escape. You also run a risk of draining the pond when the system is left running and the top freezes over. Water can easily escape the pond by running over the ice and over the sides of the pond, stream or waterfall.
Drain the External Pump
The casing of the external pump is exposed to the weather and if water freezes inside the housing it may easily crack. A drain is located on all models of external pumps to allow the pump to be drained when the system is turned off.
Drain the Filter
If you decide to turn off the system through the winter do not leave standing water in the bead filter. It could freeze solid and crack the tank, thus voiding the warrantee. Drain the filter by simply opening the drain at the bottom of the unit and allow the water to drain. Unless your bead filter is a ProBead brand you will need to somehow prevent the beads from escaping along with the water. ProBeads are designed with anti-loss drains to prevent this from happening. Unless you just want extra work we recommend you wait to perform a yearly maintenance on the bead filter until early spring because the beads are sure to clump during the months they are left idle and will need to be stirred and thoroughly cleaned before opening up the pond for spring.
If water freezes in any filter, including the Ocean Clear and BioForce brand filters, it will expand and cause damage to the casings so it’s best to drain all filters for the winter. Remember that nitrifying bacteria are not active during this time and biofilters are not needed.
Care of the Ultraviolet Water Clarifier
A few submersible UV’s are out there now and, as long as the water in the bottom of the pond is not frozen, these submersible UV’s will make it all winter without a problem. All external UV’s, however, are subject to freeze. It doesn’t matter that you’ve chosen to run your pump all year long under the premise that running water doesn’t freeze. If a storm comes and knocks out your electricity water will freeze inside the UV and cause damage to the unit.
When water freezes inside a UV it expands and cracks the delicate quartz sleeve that protects the lamp from the water. When water gets inside the sleeve it can and often blows the lamp and the transformer which all adds up in cost. We recommend that the unit be dismantled and taken inside for the winter. It’s as simple as that.
If taking the whole unit off the system is not easily done you can take out only the quartz sleeve and lamp. Aqua Ultraviolet brand UV’s (the ones in the white tubes) provides an easy answer with a cap that screws onto the end of the tube in place of the cap which fits the sleeve and lamp. This way the unit stays intact without fear of damaging the delicate glass parts inside. If the system is not running, however, the cap is not necessary.
Water Plants and Winter
Most marginal water plants and water lilies that we sell at the store are hardy for Zone 7 and will die back but then come back in spring. A few exceptions to this rule are “Ruby Runners”, “Taro” (delicate — but some come back) and “Pink Flamingo” (a variegated water celery).
Hardy water lilies are identified by flowers that float on the water and lily pads that are smooth around the edges. Tropical water lilies are characterized by serrated edges on the pads and their flowers are held high above the waterline. A blue, purple, or night-blooming water lily is generally tropical. Tropical plants and water lilies do not normally survive Georgia winters.
All water hyacinths and water lettuce (the two floaters commonly sold in Georgia) are tropical and, as a rule, will NOT make it through Central & North Georgia winters. We suggest simply throwing them away before the first frost. If they are allowed to die in the pond they will sink to the bottom and become mush. Many ask if it’s feasible to over-winter hyacinths and lettuce inside. The answer we normally give is “no” unless they are placed in a heated greenhouse with plenty of sunshine. Otherwise they become leggy and quite unattractive.
If you want to try to over-winter any water plant inside you may want to follow a few words of advice. Don’t let the roots of the plant dry out. The more sun they can get the better. Coat the leaves well with Seven dust (away from any fish) to remove any bugs that may want to make the trip inside. Water plants are hosts to many species of insects that are not good indoor living companions.
As temperatures drop most water plants begin browning out and losing leaves. Trim off these dead parts but don’t trim the green until they are brown. The roots pull nutrients from the green parts for use through the winter. This will help make stronger and prettier plants next year. Once the pots look like just pots of dirt, lower as many of these plants down to the bottom of the pond as possible. Cannas are a bit tender so, if room on the bottom is limited, make sure cannas are lowered first.
Frogs, Turtles & Toads
Survival through the winter of frogs and toads is very dependent on the type of frog or toad they are. We have, in the past, given advice to those who’ve asked about how to take care of “frogs” in the pond with answers that are very generalized. The more research we do the more we find that the term “frog” cannot be taken so generally.
Tree Frogs (those little green ones that climb) and most Toads do not depend on the pond for winter survival. They prefer moist burrows (such as toad houses) and sand to snuggle in during cold days and nights. Most of these types use shallow waters for egg-laying and prefer to stay on land.
Bullfrogs and Green Frogs depend on a collection of leaves, debris and mud on the bottom of the pond to live through the winter. This makes it difficult to have a pond that is suitable for both fish and bullfrogs. Bullfrogs prefer warmer waters and will hibernate inside the pond in the deepest part under muck and layers of leaves while that same muck creates fish health problems for koi and goldfish.
Turtles are true hibernators and, depending on the type of turtle, have special needs in order to survive the winter. Some turtles, such as snapping turtles, are great diggers and will burrow beneath the frost line in plant debris and logs. Some turtles, just like the bullfrog, prefer to snuggle in mud or a thick coating of leaves on the bottom of a pond.
Heating the Pond
If visions of mist rising from the surface of a warm, heated pond surrounded by snow is your idea of heating the pond you must be aware that it’s not an inexpensive option. Heaters are available that can keep your pond water so warm that the fish never go into winter mode. These types of heaters are similar to our home’s water heaters. Pond water is re-circulated into the heater itself then returned to the pond. Before you go out and purchase a water heater for the pond, however, keep in mind that some home heaters use copper coils that are dangerous to the fish. Special fish-safe heaters are available that do not use copper coils. The size and type of heater you need is determined by the size of your pond. We can help you choose the correct one.
To get the most from your heater you can cover the pond with a pool cover that looks like a large sheet of bubble-wrap that can be cut to conform with the shape of your pond. It holds in heat while allowing light to go through. Keep in mind that a portion of the pond’s surface must be open so gases can escape. You would also want to circumvent the waterfall or stream to minimize heat loss through exposure to cold air. Your fish will need oxygen in heated water so if you turn off the waterfall make sure to place an air stone in the water to generate oxygen for them. If you heat your water in winter don’t forget you will need to keep your biofilter alive.
Smaller heaters are available for smaller ponds (100 - 200 gallons) that look like regular indoor aquarium heaters except they are designed with ponds in mind. These are rather inexpensive and will not maintain toasty temperatures throughout the season. The power packs on these units must be protected from moisture when used outdoors. We do not recommend using a glass heater in the pond. If it were to break (and it could) you could end up with tears in your liner.
Sometimes it’s better to allow ponds to weather the winter without aid of artificial heat. If the heater cannot bring the water up to and hold it to at least 65° we can do more harm to fish than good. Water between 50° and 65° harbors bad bacteria and parasites while the fish’s ability to fight them off is low or non-existent. By keeping the water temperature at, let’s say, 62° the water certainly won’t freeze but we’ve successfully created a parasite paradise.
At 62° we’re still feeding the fish who remain somewhat interested in the world around them. They are still giving off ammonia that needs to be processed through Mother Nature’s nitrifying cycle — but there’s a problem — at 62° nitrobacter, the bacteria responsible for converting nitrites to nitrates, is weak and nitrite poisoning is a major concern.
If, by heating the pond, the water temperature remains constantly in the dangerous zone of 50° to 65° it would be much better to remove the heater and replace it with a de-icer unit instead.