Summer pond fish maintenance

This is what weve all been waiting for. Preparing the garden pond through any winter worries, ensuring that the fish have come through their rest period free from any health problems. Spring has seen the aquatic plants re-potted or trimmed if necessary and the new shoots and growth seem to be emerging from all directions.

The hard work done, the stage is set and the curtain is about to be raised on the splendour and vitality of the summer show. As summer approaches and the temperature rises each week, the pond takes on a new life of its own, as though the heartbeat of this dormant creature is about to increase as it springs into life.

Things start to happen much quicker in the pond in the summer. Plants will burst forth, perhaps spill onto the water and spread over the surface. So too will algae if not sufficiently controlled.

The pond water will also start to behave differently in these months of summer excess. The warmer weather can push oxygen to the limit, causing fish a number of problems. Various precautions should be taken to avoid stressing the ponds inhabitants, and an eye kept on various water parameters.

The fish will also enter a different stage of their calendar of development, with a heightened appetite for food, as well as each other, as the time for spawning approaches.

Even though the living should be easy in the summer time, and the pond should be thoroughly enjoyed on a daily basis, there are a number of key areas to keep a check on to make sure that your pond and all its inhabitants have a successful journey through summer. The bet advice is be vigilant, as things can grow and even progress out of hand at an alarming rate through summer.


Fish are cold blooded and their behaviour, appetite and growth rate is largely determined by the water temperature. Fish would have started feeding in spring, once pond temperatures had consistently exceeded 10oC, with their appetite improving with each rise in temperature.

Summer is a vital few months for all pondfish, as it is a relatively short window of opportunity for them to perform some essential tasks.

1. Pond fish must eat to satisfy their daily energy requirements to grow, and in addition, consume sufficient food to deposit their winter reserves.

As temperatures rise above 140C, pond fish should be offered higher protein growth diets that will fuel daily activity and growth, but also supply quality nutrition that can be stored for the autumn and winter months. If the pond fish receive sub-standard nutrition then it will not only affect the health and growth of the fish immediately, but also threaten the fishes health and survival over the winter.

2. When we feed fish, we must also remember that we are indirectly feeding the pond. It is not the end of the matter once the fish have consumed their pellets, flake or sticks as the water will be burdened by excreted by products produced by fish. In summer, when fish are feeding at their highest, waste production will also be at its highest level and this may cause water quality problems.

Filter it out.

The waste will take two forms, and must be dealt with effectively by a pond filter. A lightly stocked natural pond that is not filtered must be fed with great care to prevent the water from deteriorating.

- Solid waste must not be allowed to settle on the pond bottom where it will decompose, but should be pumped out of the pond into a filter. This will reduce the likelihood of the water becoming turbid as solid material will not be stirred up by fish.

- Soluble waste. The most toxic waste excreted by fish is ammonia, which is soluble and colourless and excreted through the gills. As it cant be seen, it can often be overlooked as a hazard to fish. However, fish produce it at the same rate at which they are fed.

A biological filter is required to break down ammonia into less toxic nitrite and then nitrates. Before increasing the feeding rate during the summer, it is essential to check that your pond is adequately filtered. Otherwise, your fish may not just be eating you out of house or home, but also themselves into health problems.

Filters is your filter in perfect condition?


As fish activity and appetites increase with temperature, so do their demands for oxygen. Unfortunately for fish, as the temperature increases, and their oxygen demand increases, the oxygen levels within a pond will decrease. This is because warmer water will hold less oxygen than cooler water. (Watch bubbles form on a kettle element when it is switched on).

To provide enough oxygen for the fish, there are several courses of action that can be taken;

1. A waterfall or fountain. Either of these water features will disturb the waters surface and mix in extra oxygen, alleviating any deficiencies. Be careful to keep the intake of the pond pump clear of algae or debris as a reduction in turnover or flow rate down a water fall or fountain will also have a knock-on effect on the dissolved oxygen levels.

2. Install an air pump with diffuser. Pond air pumps can be easily installed and fitted with an airstone at the bottom of the pond to increase dissolved oxygen and water circulation.

3. Keep at least 50% of the water surface clear of plant cove. Too many plants covering the surface of the pond prevent diffusion of air into the pond. Ponds that are home to duckweed or fairy moss can quickly become de-oxygenated, as the invasive surface weed acts as a barrier between the water and air.

Blanketweed & Algae … find the right product to solve your algae problem here

Spawning time

In the summer time the fish may be jumping for either flies on the waters surface or through the vigours of spawning activity. The summer provides a short window in which fish can breed and fry can grow to a size at which they will survive a winter.

Spawning activity in a garden pond can be quite a physical process, where the attentions of the males on a ripe female forcing her to release her eggs can result in fish becoming exhausted and damaged. The chasing and bashing associated with spawning activity can go on for many hours, and will result in many thousands of tiny translucent and adhesive eggs being deposited in submerged plants and on pond sides.

If left in the pond, the eggs will soon hatch in 4-5 days, with the fry taking refuge in the protection of the densely planted areas of a pond. Fry survival is dependent on such protection. It is not necessary to feed the fry separately as they will gain sufficient nutrition by grazing and scavenging amongst the submerged aquatic plants.


Summer represents the final scene where the last battle between good and evil takes place. Will it be victory to green water and blanket weed or will a balanced pond with healthy desirable plant growth outcompete the slimy green curse?

It is a very rare pond that has no trace at all of either green water or blanketweed. In fact, the way these two undesirable algae interact means that a pond will either show signs of one or the other. When green water is in abundance, it shades out and utilises the light and nutrients that blanket weed would thrive on. Yet if through means of an algicide or ultraviolet steriliser, the green water is eradicated, then blanket weed is likely to thrive in such conditions. If blanketweed does gain the upper hand then its growth is prolific and once oxygenators become entangled, they are unlikely to win the battle. To avoid this, blanket weed can be controlled in a number of ways:-

1) Chemical treatment. – Use of an algicide (eg Blanc-Kit) will selectively kill the blanketweed and can then be followed up with nutrient-reducing pond additives which lock away their essential nutrients.

2) Competition with plant growth. Literally, the green method, where desirable pond plants provide coverage and competition against this weed. It is preferable to allow lilies to give a pond 50% coverage, while sprawling marginals such as Water Forget-Me-Not and Parrots Feather can also provide cover from the margins. However, take care to ensure that no more than 50% of the pond surface is covered to allow sufficient gas exchange for the fish.

Top up?

Evaporation may be quite significant in extreme summer conditions, often exposing an unsightly ridge of pondliner. In extreme cases this can cause some marginal plants to dry out.

Bog gardens are particularly prone to drying out, as the submerged soil can act as a wick and draw moisture up and out of boggy areas. These too must be regularly topped up to encourage maximum plant growth.

On a fortnightly basis, besides just topping up for water lost through evaporation, it is valuable to the health of fish, especially now they are actively feeding that some of the pond water is actively removed and replaced with fresh. When water evaporates it is only pure water that is lost, leaving behind an accumulation of other soluble compounds. If the water were to be simply topped up each week, then these compounds are likely to become so concentrated as to affect water colour and fish health. As long as a maximum of 30% is changed at any one time, tap water and the use of a tap water conditioner to neutralise the toxic chlorine is quite safe.


So strange (yet predictable) is much of human behaviour, that summer is the time for 2 weeks away in the sun; leaving the pond on its own, when it is at its best (and perhaps most vulnerable).

Find a reliable neighbour with a list of things to check.

Pump pre-filter, fountain head, water level and blanket weed growth should all be on a list of things to check. To prevent a well-meaning neighbour from over feeding the fish, put a sealed portion for each day to one side for them to feed. If your holiday is anything like my experiences, then the lilies and marginals will have bloomed magnificently while you were away, and your first job is to dead-head the blooms!

In summary, the summertime is the high point of pond-keeping. When fish and plants should reward you for all of your efforts in the run up to summer. It is also a time to be vigilant, as water quality and algae problems can soon get out of control!

Kill blanketweed and string algae.