Many garden owners know the problem: In spring the garden pond looks clear and beautiful. But then comes the first summer heat wave and after some time cloudy streaks form in the water. Too many algae are undesirable in the garden pond, because in the worst case they can cause the water to tip over and the fish to die. What you can do about it, we explain here.
The most important at a glance
- The so-called algae bloom occurs when the nutrient content in the pond water is too high and the pond is exposed to high solar radiation in summer.
- Filamentous algae in particular cause problems for many pond owners, but floating algae and blue-green algae also occur.
- There are several measures you can take to combat algae. These include removing dead plant parts at an early stage.
Table of Contents
How algae develop in the garden pond
Algae in the garden pond is not uncommon. In fact, algae exist in every body of water; they are an important part of the ecosystem. A certain amount of algae even indicates a particularly good water quality.
If the sun shines steadily on the pond in summer and the water temperature rises, the algae multiply uncontrollably. An increasing phosphate content in the water also supports the formation of algae. This process is called algae bloom. Phosphate also enters the garden pond through fish feces and excess fish food. Nutrient-rich garden soil or fertilizer can also wash phosphate and other nutrients into the water. Even leaves that land on the pond water in the fall contain phosphate and thus contribute nutrients to the pond water.
Verschiedene Algenarten unterscheiden
|Algae type||How pond owners recognize them|
|Suspended algae (green algae family)||Color the water green and cloud it,|
occur mainly in the spring.
|Thread algae||Color the water green and cloud it,|
occur mainly in the spring.
|Beard algae (red algae family)||Color the water reddish and look like tufts of beard.|
|Smear algae (also called blue-green algae|
called, are actually microorganisms)
|Form dark, slimy and oily coatings.|
|Brown algae||Attach themselves to pond walls, especially|
in deeper and darker waters.
Check and lower the pH value
An increased pH value can massively promote algae growth in the garden pond. Ideal for the garden pond is a value between 6.8 and 8.2, so test the pH of the water at regular intervals using test strips.
To lower the pH value if necessary, you should regularly exchange the pond water. This also helps to control algae. The rule of thumb is 20 percent in two days. You can also lower the pH with substrates such as peat or an oak branch.
Other aquatic plants extract the nutrients from the algae
The nutrient content in the water is largely responsible for algae proliferation. To deprive the algae of their livelihood, it is important to keep the nutrients in balance. To achieve this, add more plants to the pond. Several pond plants are suitable competitors for algae:
- Water iris
- Purple loosestrife
- Water hyacinth
- Water rush
Regularly remove algae and water plants
Dead plant parts release nutrients and phosphate into the water. To prevent this process from unbalancing the nutrient levels again, generously cut back all plants on a regular basis. Remove dead plant parts as soon as you discover them. Many types of algae, such as filamentous algae, can also be easily fished off and then disposed of.
Suck off pond sludge
With a special pond sludge vacuum cleaner it is possible to vacuum off various types of algae and excess pond sludge. The advantage here is that other water plants are not damaged, but the algae are removed over a large area.
What if fish live in the garden pond?
If pond fish live in your garden pond, you must be all the more careful. This is because pond dwellers also excrete phosphate with their droppings. With the following tips, you can ensure that fish droppings do not upset the nutrient balance in your garden pond.
Do not feed from outside
The amount of phosphate in the garden pond can be significantly influenced by what the animals eat. Therefore, if possible, do not feed from the outside, but let the fish feed on what they find in the pond. Whether you need to feed or not depends mainly on how many fish live in the pond. If in doubt, it is advisable to put few fish in the pond so that you do not have to feed.
Water filters support the water quality
If you already have a lot of inhabitants in the pond, you may have no choice but to feed in addition. To keep phosphate levels low anyway, install a special filtration system. High-quality water filters remove excess nutrients and algae from the water so that the nutrient content remains in the healthy range.
Prophylaxis: Creating the pond correctly
Even while you are creating the garden pond, you are setting the first course to ensure that the phosphate and nutrient content does not increase too much. If you follow these tips, you will not have to worry so much about algae growth in the future.
Elevated space helps keep the water clean
When a body of water is in a depression, it poses the risk of garden soil or fertilizer washing in. To minimize this danger, place the pond in a somewhat elevated location.
If this is not possible, a drainage trench at least 60 inches deep will help keep garden soil out. Fill this trench with coarse-grained sand as an additional barrier.
Size and depth of a garden pond
Shallow and small garden ponds are more likely to experience an algae bloom than deep and large bodies of water because they heat up more quickly. A large and deep swimming pond, for example, usually has fewer problems with algae. Therefore, if possible, create a pond with a large volume and a depth of up to 150 centimeters (in cold regions). This will protect fish from freezing in winter and also prevent excessive heating.
Choose a shady place
The sunnier the pond, the stronger the growth of algae. This is due to solar radiation, because it favors growth. A pond should not be exposed to direct sunlight for more than about six hours a day. Make sure that at least one-third of the pond is always in the shade to avoid over-stimulating algae growth. There are floating plants that sit on the surface of the water to shade the pond. These include water lilies, frogbit and sea pot.
It depends on the content
The lower the nutrient content of the bottom of the pond, the fewer problems you will have with algae. Therefore, use low-nutrient pond soil to cover the bottom of the pond with. As for the water, the key is to check the nutrient levels and pH. Many water suppliers enrich their drinking water with phosphate, which can significantly harm the pond. Tested tap water without additives is more suitable.
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