Backyard Pond

A healthy pond requires routine maintenance. In most regions of the United States, the climate fluctuates enough between seasons that you’ll need to adapt your maintenance routine seasonally. Here, we will review best practices for maintaining your pond through each season.


Patience is critical as you prepare to bring your pond back to life. Wait until the ice melts and temperatures stabilize between 50-60. Never remove or break up ice. As eager as you might be to get your pond active after a winter lull, readying your pond for spring too soon is bad for the pond and your fish. No set month exists for spring maintenanceit will depend on your winter.

Clean the Pond

It’s essential to prioritize spring cleaning. Even after optimal pond winterization, you will find some debris in the spring. Excess organic material can create hazardous water conditions. Parasites and bacteria thrive in ponds with organic material and sludge buildup, so manually removing leaves, branches, and twigs from the water’s surface or with a pond vacuum is crucial. Similarly, using a cleanout pump or manually, you should remove debris from the bottom of your pond’s skimmer. Avoid stressing the fish by handling them or stirring up the pond too much.

Swap Mechanical Systems

Once your pond’s thawing re-exposes water to the air, you can remove your de-icers. If you were using a heater, you can wait a while longer but should turn it off before outside temperatures reach 70. Before switching on pumps, drain your filter box of any sludge build-up and ensure the media is debris-free.

If you stop your filters during the winter, you must restart the nitrogen cycle. Adding beneficial bacteria to the pond will help keep your water parameters in check. Proper dissolved oxygen levels should fall between 7 and 10 mg/L. Limit the waste in your pond so the bacteria aren’t overrun.

Resume Water Changes

Some sources recommend a full-scale pond cleaning in the spring, where you remove fish, drain the pond, scrub it, and refill it. However, we advise against this practice as it is highly stressful for the fish. This method can drastically change the water parameters when Koi are most vulnerable and introduce harmful chemicals into the pond.

Nonetheless, a water change is essential after uncirculated water sits for several months. Just limit your water changes to 20 percent, and don’t perform them multiple times within a week. Also, when adding water as part of water changes, be advised that the process lowers oxygen levels in the pond.

Gradually Reintroduce Feeding

Your Koi will be hungry after prolonged inactivity. Still, their bodies will not be ready to return to a regular feeding schedule. Typically, Koi resume eating when the water temperature is 55 to 60. When Koi become hungry, you’ll notice them swim around for food or become excited about your presence near the pond.

Start with a few pellets, and scoop out anything remaining after five minutes. Although introducing more food to the pond will not harm the fish directly, it will lead to a buildup of waste that can quickly make water conditions dangerous during this vulnerable period.

Inspect Fish

While your fish are feeding, check for signs of disease or distress. Look for ragged or split fins and tails, sores on the body, lifted scales, or patches of discoloration. Fish are most susceptible to illness after winter because the dormancy weakens their immune systems. Having emergency staples on hand in case of a bacterial or parasite outbreak is a good idea. Potassium permanganate, salt, and topical antibiotic ointment are a few options. However, you should not use these remedies as preventatives. Unnatural additives can disrupt the pond’s equilibrium.

Limit Aeromonas

A temperature danger zone, often called Aeromonas Alley, occurs when pond water is between 50 and 60. Though these opportunistic pathogens, in moderation, perform a valuable service by feeding on your Koi’s waste, at these temperatures, they multiply much faster than the fishes’ immune systems restore themselves. In fact, given the right environment, a single live Aeromonas cell can replicate to 30 million in one day.

Because the optimal temperature for a Koi’s immune system is about 73, a significant period will occur when the fish are highly vulnerable. No matter how good your water parameters or how hyper-vigilant you are, other vectors can introduce bacteria into your pond. To make things worse, many common parasites such as costia, chilodonella, trichodina, and flukes grow simultaneously.

Water the Water Quality

A significant change in the pond environment can also spark changes in water quality. Spring is a necessary time to closely monitor pH, nitrate, nitrite, and alkalinity levels. The good bacteria that live in your pond and filter (Nitrosomonas and Nitrobacter) that break down harmful ammonia and nitrites multiply very slowly compared to other bacteria, especially in cool water.

A safe ammonia level is as close to 0.0 as possible. At just 0.15 ppm, your Koi can experience significant health effects, including tissue damage and bacterial or parasitic infections. Although not as deadly as ammonia, nitrite concentrations above 0.15 ppm can cause critical illness in Koi. Nitrites will prevent a Koi’s red blood cells from absorbing oxygen. The ideal range for nitrate is 20-60 ppm. If the pond’s levels reach 80 ppm, you should begin a regimen of partial water changes and daily testing. Nitrate will become toxic to fish at 120 ppm.


The pond’s most active season is a favorite for many Koi keepers and their friends and families. However, the water parameters can quickly become problematic in the summer between higher water temperatures, undigested food, and increased waste. Test water regularly for pH levels, ammonia, nitrites, and nitrates, all of which can harm fish when out of balance. Water testing frequency depends on the pond size, number of fish, and quality of the filtration systems. Still, the frequency of testing should be highest in the summer.

Avoid Overfeeding

Koi are more active during the summer and will eat more food, but be careful not to overfeed. Excess food accumulates in the pond and can cause significant water quality problems. Your summer temperatures will dictate the number of times you feed per day, which typically should be one to three, depending on where you live. Feed only as much as your fish will eat in three to five minutes. If you are hosting and know your guests want to feed the fish, schedule that into the routine rather than adding it on.

Increase Aeration

As the pond water warms, it loses the capacity to hold oxygen. In the summer, you must put maintaining water levels high on your priority list. Your Koi require oxygen levels of at least seven ppm. Readings below three ppm will stress the fish and lead to behavior changes, disease susceptibility, and even death.

Several options exist for increasing oxygen levels. An aeration pump can increase oxygen saturation and help bacteria do their jobs. A bottom drain is helpful because it pulls the water with the lowest oxygen content to the surface. Air pumps and stones are additional options for increasing aeration in summer. Fluid bed filtration technology is another way to aerate a Koi pond. This involves sending air into a basin filled with bio media, providing an oxygen-rich environment for your Koi.

Keep an Eye on Algae

While some algae in the pond are normal and beneficial, an overgrowth can create problems in your pond’s ecosystem. Longer hours of more direct sunlight can cause algae to overpopulate in the summer. An abundance of algae will consume more oxygen than it creates, which is problematic because your Koi require more oxygenated pond water in the summer.

If your pond has large algae blooms, the best preliminary step is to scoop, rake, or vacuum the bulk before treating the rest. This process can be time-consuming and not a long-term solution (the algae will grow back). However, it can create a more manageable situation for you to work with as you address the underlying causes of the algae growth.

Provide Plant Cover

Aquatic plants help aerate and cool the pond, contribute to biological filtration, and provide protection and shade from the sun. The presence of plants also helps keep algae levels in check. Three categories of pond plants are floating plants, shallow water marsh plants, and submerged plants. Different plants might be more suitable than others, depending on where you live. In nearly every region, some common aquatic plants are water hyacinth, water smartweed, water lotus, water lettuce, and water lily. Strive for plants to cover at least one-third of your pond’s surface in the summer.


The warmer summer months will accelerate pond water’s natural evaporation, especially in more arid climates. Lowering the water levels is akin to adding Koi in terms of the available space for each fish to swim. Remember that a water top-off does not factor into the percentage of water you change each week, which should range from 10 percent to 20 percent, depending on your water parameters.


Your main task as a pond owner in the fall is debris removal. As leaves start to fall, having a netted cover across the pond’s surface is extremely helpful in catching foliage before it gets into your pond. Carefully roll up the net and discard the leaves that are trapped. A high-quality pond vacuum also helps clean debris or waste that filters or drains might have missed.

Trim Plants

Trimming your plants helps prevent organic debris from entering the pond. For leafy plants surrounding your pond, use pruning tools to cut away dead foliage and move them deeper into the pond. Bog plants can be left alone.

Reduce Feeding

When outside temperatures drop below 65, it is time to start slowing down your feeding schedule. You can do this gradually by reducing the number of meals per day, then every other day, and finally just a couple times per week until temperatures are consistently lower than 50 when you can stop feeding altogether. Switch from a higher-protein feed used during the summer to a low-protein, high-carbohydrate diet during the fall. A cold-water wheat germ-based food will be easier for Koi to digest.


If your pond contains a skimmer, empty the liquid from the box and slightly lower the pond’s water level. Removing it from the pond is unnecessary, but water trapped inside can break the equipment as it freezes. Wash the filter media pads, disassemble UV clarifiers, and clean and inspect your pump. Keep the pump, filters, and clarifiers in a location that will not freeze.

Beneficial Bacteria

Some Koi keepers believe fall is the time to introduce cold water beneficial bacteria to the pond once temperatures drop below 60. These bacteria will consume sludge at the bottom of the pond, reducing the amount of organic material before winter. However, some enthusiasts argue it’s unnecessary if your pond is well managed.


How to best maintain your pond during the winter largely depends on where you live. In warmer environments where you’re unlikely to experience freezing temperatures, you will continue managing your pond as in the fall. In most parts of the United States, where temperatures either regularly or intermittently drop below freezing, you must make a few adjustments.

Pond Cleaning

You will want to clean your pond one last time before shutting it down for winter. Clear out your skimmer and ensure your pond is free of leaves and debris. Consider covering your pond with a net to prevent debris from building back up over the winter.

Turn off Equipment

You must decide whether to keep your pond running for the winter or turn off equipment. Shutting down is recommended in colder regions. If you have multiple pumps, you may only have to stop some of them. However, Koi need peaceful waters in the winter, so you must ensure that water does not move and push the Koi too much, as they will be in a state of hibernation. If you stop filters, drain all water. If you leave water in them, they will hold rot, waste, and sludge.


The good news is that it is rare for a pond to freeze completely solid. Ponds freeze from top to bottom, so a layer of ice on top of the pond acts as insulation that usually prevents the lower water levels from freezing. The bad news, however, is that Koi cannot survive in solid ice. So if your pond freezes and you haven’t taken precautions, you risk killing your fish.

Without water flow, oxygen levels will fall, and ammonia and other harmful waste will build up. An aerator or a de-icer in your pond should be enough to keep the surface from freezing. If you don’t have them, you will have to create an opening in the ice in the event of an unexpected freeze. Do not break the ice, as the vibration of shock waves this sends through the pond can harm your fish. Instead, set a pot of hot water on the ice and allow it to melt a hole through the surface gradually.

In addition to ice-prevention equipment, a few do-it-yourself tricks can assist in ice prevention. One option is to place a few tennis balls or a beach ball in the water. The motion of the balls will help keep the water moving and prevent it from completely freezing. An empty two-liter soda bottle or a pool noodle can also do this. Installing protective netting over your pond can help keep the surface of your pond free from leaves and other debris, which will help limit the build-up of waste if your pond becomes ice-capped.

Thinking about adding a new fish to your pond? Browse our selection of Koi and Goldfish.

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