A well-balanced water garden requires relatively little maintenance. Occasional cleaning and frequent checks on its equipment and water level are about all that is needed. Unless there is a lot of accumulated debris that can not be removed by other means there is no need to drain the pond on a regular basis and disturb the ecological balance within it. Instead, use a net or pond skimmer to remove falling leaves and other plant debris, i.e. dead waterlily blossoms and leaves, free-floating algae, etc. Dead plant material that has accumulated at the bottom of the pond must be removed. Not only does a clean pond look better but it is also healthier for it and its occupants. Decomposing plant material can smell and it pollutes the water for all the other aquatic life.
If you do drain the pond, refill it immediately after cleaning but allow the water to warm up before adding your plants. Cold water may shock some tender plants. Allow the pond to re-establish for two to three weeks before adding fish.
A major clean-up requiring draining of the pond is the only time when it becomes adviseable to add a large quantity of fresh water to your pond. At all other times we recommend to add small amounts of fresh water only. Keep an eye on the water level and top up the pond when needed, being careful not to alter the water temperature by more than a few degrees. Some people prefer to collect rain water in barrels. The rain water can then be added to the pond as required. This is especially useful if you are on municipal water that is chemically treated.
Algae control is usually the largest maintenance problem in a pond. When setting up a new pond it is normal to have excess algae growth until an ecological balance has been achieved. This balance is achieved through the right proportion of floating, marginal and submerged plants, fish, and scavengers (snails and tadpoles). All plants provide oxygen and consume nutrients in the water. Submerged (also called oxygenating) plants are beneficial because they produce especially large quantities of oxygen and provide supplemental food for fish as well as a place to spawn. Floating plants are most beneficial for providing shade (important for keeping the water cooler - cool water holds more oxygen and is healthier for your fish), preventing water evaporation, and providing hiding places for the fish. Marginal or bog plants provide hiding places for small fish or scavengers and shade in the early morning or late afternoon. Fish excrement, once broken down, provides nutrients for the plants. Oxygen is converted to carbon dioxide by the fish. They also consume insect pests and a little algae, too. Scavengers consume algae, decaying plant material and fish waste, thereby providing nutrients for the plants. It is a complete cycle with each element depending upon the others to provide what they need to survive.
A little algae is natural, will always occur and is necessary for a healthy pond but too much can be detrimental. The amount of algae in your pond depends on the weather, the amount of sunlight, the temperature of the water, the amount of oxygen in the water and the number of nutrients and different kinds of plants present. It can be at its worst in the spring. This is because the algae does not have any competition yet. The situation will most likely clear up once all the plants have started growing again. Be patient. If it doesn't clear up on its own, something is out of balance. The easiest solution is to add more plants. Both algae and water plants compete for the same sunlight and nutrients in your pond. Adding plants can make the nutrients unavailable to the algae, and increasing the amount of surface area covered by waterlilies and floating plants can decrease the amount of sunlight available for the algae. This is of particular importance if your pond is small and shallow. Having only a few plants
in an open expanse of water combined with sunlight will result in warmer water and increased algae production.
If you have a lot of plants and still have too much algae then perhaps there is an excess of nutrients in the water. This could be caused by a number of different factors or a combination of them. One of them could be a run-off problem. Check to make sure that garden or lawn fertilizers are not washing into the pond when it rains. Perhaps you are over-fertilizing your waterlilies or doing it incorrectly. Maybe you have too many fish, and their excrement is causing a nutrient increase. Maybe you are overfeeding your fish. A pond filter/UVC may help to lessen the impact of single-cell-free-floating algae. This is the type that gives your pond the appearance of pea soup. You can also use chemicals to control this type of algae. It is a short term solution and will not eliminate the reason the algae is growing in the first place.
The amount of oxygen in the water is also important. Algae, as a plant, needs carbon dioxide to survive. The higher the oxygen levels, the lower the carbon dioxide levels will be. Oxygen is needed in the water to support aquatic life like fish, tadpoles, as well as aquatic snails, all of which eat algae.
If your fish are coming to the surface gasping for air you have a problem in your pond, namely an oxygen shortage. You can increase the pond's oxygen levels by adding an aerating nozzle on a pump, planting more oxygenating plants or adding a bit of fresh water.
When water is exposed to air it will pick up essential oxygen. Other than for aesthetic reasons this is why many people use a recirculating pump to run a waterfall or fountain head. Moving water is aerated water.
Blanketweed or filamentous algae is another common problem in ponds. It has been suggested that blanketweed is the sign of a healthy pond as it removes excess ammonia from the water. A pond with blanketweed almost always has clear water. Little consolation to the person whose pond has it. The most common solution is to simply pick it out. There are chemicals available, like Interpet's Pond Balance, that do not harm your pond and help eliminate blanketweed (you will still have to pick the old stuff out). Another way to reduce blanketweed is to install a magnet. No one is entirely sure why this works. For best results, the pH of the pond should be between 7.0 and 7.5.