Summer Pond MaintenanceSummer is the high-point in the water-gardener’s calendar – a time when the pond should be at its best and plants fish and wildlife thrive, bloom and breed; in short, summer is payback time for all the planning, planting and sheer effort involved in getting this far in the first place. At the same time, those long sunny days and hot, humid nights can bring challenges of their own for the unwary pond-keeper, so alongside the justifiable enjoyment of the fruits of our labours, we also need to keep an eye out for signs of trouble. The warmth means things can change very quickly in the pond and, if the early signs are missed, problems such as algal blooms and deteriorating water quality can soon become major summertime headaches. With a little bit of vigilance and a spot of careful summer maintenance, however, we should be able to avoid having our enjoyment spoiled too much. Year round pond maintenance is important, and we have guides for Spring. Autumn, Summer and Winter

Water Quality

Changes in the pond and the behaviour of its inhabitants during the warmer weather can make water quality problems more likely, principally in terms of dissolved oxygen and nitrogenous waste – both of which are particular nuisances for ponds stocked with fish.

Oxygen dissolves naturally in water, but how much oxygen water can hold depends, amongst other things, on temperature; in short, the warmer the water, the less dissolved oxygen (DO) it contains. This is, clearly, a potential problem during the summer, since low DO levels precisely coincide with the time when fish require the most oxygen. In a well stocked pond particularly, this may cause a problem for the inhabitants, especially if it is well planted. Although an adequately sized waterfall, cascade or fountain should ensure that sufficient is added to meet their needs, it is important to remember that while plants contribute abundant oxygen to the water during daylight, they themselves use it at night. A heavily planted pond – or one full of algae – can develop seriously depleted oxygen levels as dawn approaches, especially if the previous day was a very warm one.

Pond Air Pump

Installing a pond air pump with a diffuser stone – a giant version of the familiar aquarium set-up – can help, as can ensuring that at least half of the surface area of the pond is open to the air. Ponds covered in duckweed or fairy moss, for instance, tend to have little natural oxygen diffusion – so be ruthless when it comes to clearing out invasive plants.

As the water temperature rises, fish – being cold-blooded creatures – become more active and need to eat more as a result. This leads to larger amounts of waste being produced – fish turn around a twentieth of the food they consume into ammonia – which inevitably places greater strain on the filtration system. In addition, since fish need to fuel their current activities while also gaining enough reserves over the summer to see them through the coming winter, the sensible fish-keeper will provide high protein food once the pond water reaches 14 degrees C.

The higher the protein level, the more ammonia produced – potentially putting what is a prudent summer feeding regime on course to drive elevated ammonia and nitrate levels in the pond. While it is obviously essential to install a bio-filter which has sufficient capacity – and some to spare – to deal with the volume and stocking levels of your pond, the only way to be certain that your system actually is doing all that is demanded of it is, once again, to test the water to make sure. While ammonia and nitrite levels around zero are, of course, comforting, high nitrate readings bring their own potential problems.

Green Water and Blanket Weed

As the days get sunnier and nitrate levels rise in the pond, there is the ever present danger that algae – either the “green water” variety or the long strands of blanket weed – will appear. Nourished by excess nutrients coming from left-over fish food, fish faeces and rotting plant material, algae can be a major problem – especially if they are allowed to become established. Fortunately, with the development of ultra violet clarifiers and a whole range of chemical, organic and technological control measures, neither green water nor blanket weed should pose a permanent problem – especially if the elevated nitrate levels are spotted early enough.

The ideal summer pond should involve little more than checking the water level for evaporation and topping up as necessary or thinning out floating and marginal plants, as and when required. After all, it is summer time and the living is easy – or so the song goes – and with vigilance and a little judicious maintenance, it should be possible to make sure that it stays that way.


During the summer, your pond will require additional maintenance due to increased activity from your koi. It’s crucial to maintain water quality as warmer temperatures and increased waste production can cause water parameters to quickly become an issue.

Here are some summer tasks to help maintain a successful pond season:

  1. Test water quality at least twice a week to ensure it remains within acceptable levels.
  2. Perform a 10-20% water change weekly to keep the water fresh and healthy for your koi.
  3. Monitor dissolved oxygen levels since they tend to be lower in warmer temperatures. Adding an additional aeration device can help improve oxygen levels.
  4. Provide ample shade for your pond to prevent sunburn on your koi and prevent water temperatures from getting too hot.
  5. Clean and flush your filters at least once a week to maintain good water quality.

Adding pond plants

Adding more aquatic plants to your pond during the summer months can help improve water quality. Plants absorb nutrients that would otherwise contribute to algae growth, and they also provide shade and shelter for fish. Consider adding floating plants like water lilies or submerged plants like anacharis or hornwort.

Controlling algae

In addition to UV clarifiers and chemical treatments, there are natural ways to control algae in your pond. Adding beneficial bacteria products can help break down excess nutrients and prevent algae growth. You can also manually remove algae using a net or rake, but be careful not to remove too much at once and disturb the balance of your pond.

Preventing evaporation

Hot summer temperatures can cause water to evaporate from your pond more quickly, which can lead to low water levels and potentially harm your fish. Consider adding a pond cover or shade cloth to reduce the amount of direct sunlight hitting your pond. You can also add a water feature like a fountain or waterfall to help aerate the water and reduce evaporation.

Feeding fish adjustments

During the summer, you should adjust your koi’s diet to account for their increased activity and metabolism. Offer them high-protein foods like pellets or live insects to help them grow and stay healthy. However, be careful not to overfeed, as uneaten food can contribute to poor water quality.

Protecting fish from the heat

As the weather gets hotter, it’s important to monitor your fish for signs of stress or illness. Heat stress can cause fish to become lethargic or exhibit unusual behaviors. Adding more shade and aeration to your pond can help keep your fish cool and comfortable. You can also add salt to your pond to help prevent parasitic infections.

Monitoring pond pH levels

pH levels can fluctuate during the summer, especially in ponds with high levels of biological activity. Test your water frequently and make adjustments as necessary to maintain a pH level between 7.0 and 8.5. Adding a pH buffer can help stabilize the pH in your pond.

Cleaning pond debris

Summer storms can bring debris like leaves and twigs into your pond, which can contribute to poor water quality if left unchecked. Use a skimmer or net to remove debris from the surface of your pond. You can also vacuum the bottom of your pond using a pond vacuum or a wet-dry vacuum.

Checking pond equipment

Your pond equipment, such as filters, pumps, and aerators, will be working harder during the summer months. Check them regularly for signs of wear or malfunction, and replace any parts as needed. You should also clean and maintain your equipment to ensure it continues to function properly.

Last Modified: April 6, 2023