Introduction to Pond Fish
Ponds need regular maintenance if they are to provide fish with a healthy and safe environment. Problems are most likely to arise in the first year, before the pond is established, and are typically caused by overfeeding or overstocking. Frequent monitoring and an awareness of seasonal changes will help avoid the major pitfalls.
As fish begin to stir out of their period of winter dormancy, spent in the depths of the pond, they are very susceptible to minor illnesses, such as bacterial infections, which can rapidly overwhelm their weakened immune systems. Thorough inspection of individual fish will help identify and treat illnesses in their earliest stages (see pp.322–324). Once the water temperature increases, fish regain their appetites and become better able to fight infections. This surge in appetite, and the resulting increase in waste products, causes a rise in ammonia levels in the water, so now is a good time to maintain and service filtration equipment. The beneficial bacteria in biological filters are inactive during cold weather, and such filters may need to be reseeded with bacterial cultures. Live and freeze-dried cultures are available from suppliers of pond equipment. The addition of zeolite, a chemical that absorbs ammonia directly from the water, may also be beneficial until the filter is fully functioning again.
Pond fish begin to show spawning behavior in late spring, when new plant growth provides surface cover for the fish and for any eggs and resulting fry in the pond. Check regularly in case any fish have become trapped in reeds or other plants or any females have been driven out of the pond by overenergetic males. During the summer, the increased temperature of the water and greater activity levels of the fish result in lower oxygen levels. If not controlled, plant and algal growth also reduces oxygen levels in the water. To maintain oxygenation, fountains and other water features should be left on overnight, or special aeration equipment should be installed.
Preparing for winter
Pond plants begin to die back in the fall, and excess foliage should be removed. Falling leaves should not be allowed to accumulate on the surface of the pond, because they decompose in the water and can harm the fish. Covering the surface of the pond with netting keeps leaves out of the water and allows them to be collected easily.
If there are delicate fish in the pond, or any young from a late spawning, they should be caught and transferred to an aquarium for the winter to ensure their survival. When the water temperature falls below 43°F (6°C), the remaining fish may enter an almost completely motionless state and will not require feeding until spring. Below around 39°F (4°C), a warmer layer of water will develop in the deepest part of the pond, where pond fish spend the winter. If there is a submersible pump installed, position it more than 6 in (15 cm) from the bottom of the pond, and switch off water features, such as waterfalls or fountains—otherwise, these will circulate and cool the water by mixing the colder surface layers with the warm layer below.
In mild areas, a pond heater can help to prevent the surface of the pond from freezing over in the winter. It will stop the area around the heater from freezing, allowing noxious gases produced by decomposing plant matter to escape from under the ice. If ice has formed on the surface of the pond, never try to smash it, because the shock waves will traumatize the fish and may even prove fatal. Instead, melt the ice slowly by carefully holding a hot saucepan on the surface of the pond.
SEASONAL PLANT CARE
Plants around the pond may benefit from a layer of leaf mulch to protect them in winter. Plants in the pond itself that are vulnerable to freezing weather must be transferred indoors before the first frost. Although the winter pond may look bare (below left), the plants can be returned to the pond in spring and will grow quickly over the summer (below right).
- Removing leaves in the fall is easier if netting is placed over the surface of the pond.
- Algal blooms—sudden flushes of algal growth— can be a problem in warm weather. Removing any dying or dead leaves from plants around the pond will help limit algal proliferation.
- Blanketweed is a type of filamentous alga, which can trap fish. It should be removed regularly using a stick.
- Duckweed grows rapidly and will entirely cover the surface of a pond. It can easily be controlled by scooping it off the surface.
REGULAR MAINTENANCE TASKS
- Check to see if fish are showing signs of ill health or behaving strangely.
- Ensure that the filtration system, if present, is functioning correctly.
- Feed the fish, according to their appetite, several times during the day, except in the winter or in very hot weather.
- Note the water level in the pond; sudden falls indicate a leak in the pond liner.
- Monitor the ammonia and nitrite levels, especially in a newly established pond.
- During the growing season, remove faded flowers of marginals, unless seed is required.
- Top off the water level in the pond if the evaporation level is high, using water treated with a dechlorinating product.
- Test the oxygen levels in the water, especially in hot weather.
- Check for any signs of plant pests, such as aphids, removing them from the vegetation where necessary.
- Check the nitrate level of the pond water. It should not rise above 50 mg/l.
- Remove blanketweed so that it cannot choke other plants and pond fish.
- Prevent any buildup of algae on bridges or decking, which could make them slippery. Remove it by scrubbing the surface of the wood with a clean brush.
- Watch for any signs of moss growing on the surface of paving or stepping stones close to and surrounding the pond.
- Rather than stocking the pond to the maximum capacity at the outset, add further fish gradually over the spring and summer months.
CLEANING OUT A POND
Over time, sediment accumulates in the pond, and plant growth proliferates, inevitably reducing the area of water that is accessible to the fish. At intervals of a year or so, it is a good idea to unertake a major clearout. The best time is in early spring, because the pond will have time to reestablish itself in the warm summer months. If any cases of serious illness have occurred within the pond, it may require disinfection. Some preformed pond units can be lifted out of the ground to make this task easier.
- Before starting the clearout, catch the fish and move them to a location where they will be safe.
- Siphon or bail out the pond water, removing other aquatic life, such as snails or dragonfly larvae.
- Divide and repot water lilies and marginal plants.
- Remove the silt using a spade or scoop, and hose out the base of the pond. The used silt can be dumped on flowerbeds.
- Refill the pond, adding a suitable volume of water conditioner.
- Allow the water temperature to rise before returning the fish and
plants to the pond.
- Remove the fish before cleaning, watching closely for small fry; transfer the fish to a safe container.
- Reintroduce the fish only after any replanting is complete; allow the fish to settle without further disturbance.
- The surface of a pond can become choked with aquatic vegetation (top). Clearing out the pond, by thinning or cutting back the plants and removing dead matter, provides the fish with a larger swimming space and makes the area neater, safer, and more attractive (bottom).