If you’re fortunate enough to live near a natural pond and have spent time during the year observing it, you know that natural ponds endure the seasons quite well. From the frozen dead of winter to the intense heat of summer, they maintain a biological balance that ensures the continued existence of the plants, animals and insects that depend on them.
The same cannot be said for ornamental ponds. Besides the fact that most ornamental ponds are significantly smaller than most natural ponds, the life contained in them has been added by the pondkeeper and rarely represents local native fish or vegetation. And the ratio of fish to plants is typically the reverse of natural ponds — as much as 90 percent of the biomass in a natural pond is plants, not fish.
For pondkeepers, this means all kinds of issues in terms of maintenance, fish health problems and the dreaded scourge of pondkeeping: algae. As the seasons change, the problems change. The good news is that to a significant degree, these issues can be minimized with some planning and attention to details.
It bears mentioning that climate change is already having an effect on when the seasons begin and end, and on how erratic the normal weather patterns can be. Winters, for example, can be milder at times, affecting the duration and amounts of ice and snow.
We’re starting with spring because that’s when most people build and stock their pond. You may have wondered about the reference to five seasons instead of four in the subtitle of the article. For our purposes, there are two springs when it comes to new ponds. The first spring and the following spring are different because of the changes that occur in any pond after its first full year, so we want to look at both.
A new pond is like a new aquarium. It’s missing the biological essentials that are basic to all healthy aquatic environments. So, in some ways the first season of a new pond is like initially cycling an aquarium, except pond fish tend to be hardier, and there will (should) be fewer of them, relative to the size of the water volume. Populations of certain bacteria need to increase until there are enough to handle processing the ammonia and nitrite in the water from fish wastes. Careful stocking levels of fish are therefore important, and because pond fish become larger in length and mass than most aquarium fish, modest stocking is therefore doubly important.
As the water warms from direct sunlight, the rates of biological activities within both the pond and the fish increase. Even a lightly stocked pond with fish that are not overfed may develop some green water. Green water is the result of a rapid population increase of single-celled algae as nutrient levels in the water increase with warmer temperatures. In a new pond, this typical springtime phenomenon is moderate and brief.
Frankly, this first season is relatively easy. Making sure everything is running properly and getting into a routine for feeding the fish, cleaning the filter and maintaining water level are the more important issues. Otherwise, there’s little to do but watch the fish and plants grow as spring passes toward the start of summer.
By the time summer officially begins in the latter half of June, the pond might seem almost too easy to take care of. You may not feel this way, however, a month later when pond temperatures are up and algae are seemingly everywhere. This is the season that tests the pondkeeper’s will and resilience. The combination of increases in temperatures, sunlight and nutrient levels in the water causes algae to grow. This algae will be long, stringy algae rather than the unicellular algae of green water.
The primary reason for this growth is an excess of nutrients in the water, the result of the previously mentioned difference between natural ponds and ornamental ponds. Essentially, plants make up the greatest proportion of life in a natural pond, whereas fish are the majority of biological load in an ornamental pond. When there are a lot of plants, they use up much of the nutrients in the water, and these nutrients are also at lower concentrations because there are fewer fish. The reverse is true in a typical home pond, so algae can only be controlled — maybe — by removing it from the pond. Removing algae is a lot of work. It’s messy and is only a temporary solution during the warmest months of the year.
If July seems bad, August is worse. The only way to reduce nutrient levels, other than having a lot of plants and/or having fewer fish and feeding them less, is to do large water changes. However, with a pond this is a significant undertaking and not even possible where drought regulations are in effect. If the pondkeeper can survive the ordeal of summer algae, the rest of the pond year will seem easy by comparison. But many don’t, and more ponds are filled in for this reason than any other.
Call it fall or autumn — this is the season that is spring’s opposite. As with spring, the start of this season varies from region to region. When the weather begins to cool and the nights become even cooler, biological activities slow down. The lower temperatures and reduced sunlight as the sun’s path moves south bring an end to summer’s algae nightmare. When water temperatures reach, and then stay in, the low 60s Fahrenheit, the fish will need less food and the plants will need less pruning.
Cold nights will cause water temperatures to decline even if the days are sunny and sunlight can reach the pond. When water temperatures stay below 60 degrees, you can stop feeding the fish. Their metabolism is controlled by their body temperature, which is in turn controlled by water temperature, so they will use less food in cooler water and may stop metabolizing it when the water is in the 50s. Do not feed while the fish are kept at these low temperatures.
The most important fall tasks for the pondkeeper are directed toward preparing the pond for winter. Non-native plants will not survive freezing water or air temperatures, and tropical species will not likely survive for long in water that’s in the 40s. So choices have to be made.
Plants that will not survive the winter must be brought inside. “Inside” can be a basement or perhaps a garage that will not approach freezing. The plants are wrapped in burlap or layers of newspaper and become dormant. This is enough work that it might make some pondkeepers consider stocking the pond with native plants, which will overwinter without problems, regardless of freezing weather.
Even more work is bringing in the fish. Yes, pond fish can survive winter outdoors — sometimes. But some do not live to see spring, while others simply never do as well, even if they survive. If fish die in near-freezing water, there’s no biological activity such as decay. As the water warms in late winter, this will obviously change. Ponds must be deep enough that there is sufficient water below the frost line for the fish to survive. This is no guarantee, however, when winters are unusually severe and the water freezes to the bottom.
Bringing in the fish is the only real solution, and this requires a vat (or more) of water of sufficient volume to sustain the fish and filtration to maintain good water quality. Each fish must be transported in water to the vat, which is typically located in a basement, but it can be in a garage or other building that is warm enough. As the fish grow larger and the amount of water in which to transport them increases, the weight of the container becomes greater each year. Family members and friends are needed to help drain the pond, capture the fish and move them to their winter home. If the weather is cold enough during this, splashed water will quickly freeze, making paths and steps even more treacherous.
Some people purchase heaters to keep the pond from completely freezing over, but these are expensive to run in terms of electricity, and the fish may still not do well. In areas with less severe winters and only an occasional night with frost, the fish can remain in their pond during the winter, but should not be fed or disturbed. Even in areas with mild (but not tropical) winter weather, the water will become quite cold. In southern California, for example, the water can remain warmer than the air temperatures on sunny days. However, it’s most likely that pond water will be about 48 to 50 degrees on cooler days, and it is best to not feed at all when water temperatures are consistently this cold.
This is the season of pondkeeping with the least amount of work. The elements of winter will turn ponds into frozen, snow-covered bodies of ice, except in more temperate locations. If the fish are indoors, you should seriously consider emptying the pond. Ponds with quality liners may be fine if they are padded from any underlying rocks that might move as a result of frost heave, but concrete ponds and those above ground will likely suffer damage from expanding ice. Cracks or worse are not uncommon.
For ponds, winter can be from November through March in many regions, and even longer some years. Ideally, the fish should be removed when temperatures are in the 50s, and they should stay in their winter home until water temperatures are consistently in the low 60s. Conceivably, the fish could be removed as early as October and not be returned to the pond until late April or even early May.
This is the “fifth season” — the one that is rather different from the first one. With fish and plants back in their now-warming home, there is a race between two biological processes. The fish are coming out of winter with depressed immune systems, the result of little or no food and the stress of colder water (keep in mind that pond fish are coolwater animals, not cold), and they will be larger than in the previous spring. Even if the fish were brought inside, they will still have compromised immune systems. Given the much slower biological processes in fish kept in sub-optimal water temperatures (such as unheated vats kept in a garage), they are slower to respond to disease-causing organisms during those first weeks when the water is warming.
At the same time, the bacteria that make biofiltration possible are fewer in number and inactive as a result of cold temperatures and no food (because the fish have not been eating or perhaps weren’t even in the pond). This means that ammonia and nitrite levels will be higher than normal for several weeks, adding to the physical stress on the fish.
In the meantime, the pathogens in the water that cause disease in fish are seeking hosts as the water warms. The fish that have less effective immune systems during the first critical weeks of spring may succumb to disease. So, the likelihood of fish health issues can be higher — more so if the pond is overstocked and/or the fish overfed. Good water quality is the most important factor in minimizing this possibility.
Once the water has reached the upper 60s and low 70s, the fish will be active and hungry, and all biological processes will be up to speed. During the first spring, as discussed, mild problems with green water could occur if there were sufficient nutrients in water that was becoming warmer and exposed to sunlight. By the second spring, the nutrient levels are much higher, a result of both residual concentrations from the previous summer and the greater amounts of wastes from the now-larger fish. Green water is almost inevitable at some point during the spring.
This time, instead of a light green, the water may begin to look like pea soup. Although not harmful to fish, pondkeepers tend to dislike the appearance of their pond during green-water season. In a healthy ornamental pond the problem should run its course in a week or three, as long as the fish are not fed too much. Controlling nutrient levels in the water is just about the only solution other than an ultraviolet (UV) sterilizer.
UV sterilizers have become popular because they can effectively kill unicellular algae as water passes between the sterilizer’s housing and the UV bulb inside. The only limiting factor is how much water can be processed per hour, because the rate at which it flows through the sterilizer is dependent on the wattage of the bulb. Higher wattage bulbs — which are larger and thus make the cost of the unit more expensive — can process more water and kill more algae. These units are placed in-line with the filtration system.
The seasons of a pond are both predictable and yet variable. The health of the pond as an aquatic environment determines the health of the fish and all other life within the pond. The heating and cooling of the water, nutrient levels and the amount and duration of sunlight are all factors that vary from season to season.
As the fish grow, the issue of nutrient levels will also grow and will perhaps require reducing the number of fish. The addition of plants — the more the better — can reduce algae issues and improve overall water quality. Choose those that are native to ponds in your region so they can both overwinter and begin to consume nutrients as the water warms.
You will come to use the pond as an indicator of seasonal changes, much like turning leaves and budding flowers. Its charm and beauty will change as each season comes and goes.
Miller Morgan writes about aquariums and fishkeeping from unique perspectives to give readers a broader appreciation for the hobby.