Filamentous algae are the most feared type of algae for garden pond owners. The thready, fluffy structures not only disturb the visual appearance of the pond, but can also pose a serious threat to pond inhabitants. So arm yourself with the necessary knowledge about the pests.
Filamentous algae make the pond water appear green
How to recognize thread algae
Algae are present in every garden pond. The most common, however, are blue and green algae, which can hardly be identified due to their microscopically small plant bodies. They also pose a rather minor threat to water quality.
Thread algae, botanically Zygnema, are much more problematic. This is an entire genus within the green algae. Therefore, they can visit your pond in different forms. For example as:
- Long, branched, green threads
- Fur-like, cottony coating on the water surface
- Tufts that also grow over stones
The problem with thread algae is that they grow at low water temperatures from 5°C and can spread very quickly. This increases the risk of rapid clouding of the water. If you do not act in time, algae blooms can quickly occur and the pond is in danger of tipping over. The rapidly developing mass of algae then soon dies due to the depletion of nutrients and sinks to the bottom.
The algae residues consume a lot of oxygen, which can cost the lives of any fish, insect larvae and amphibians. The submerged algae then release nutrients into the soil and the water again at the bottom of the pond, which can lead to new algae growth.
What to do against thread algae?
preventive measures
In order not to let it get that far in the first place, there are a number of things you can do in advance. Basically, the best preventive measure is not to let the nutrient content in the pond water get too high. You can achieve this by:
- Fish the fallen leaves off the water surface regularly
- Plant a lot of pond plants for nutrient utilization - they deprive the filamentous algae of the basis for colonization
- Do not overfeed any fish stock - excess fish food unnecessarily increases the phosphate and nitrogen levels in the water!
- Interrupt possible swathes of (fertilized) flower beds that have been washed into the pond water
- Put algae-eating fish in the pond: Silver or grass carp, for example, are willing to destroy thread algae
emergency aid
If it is already too late and filamentous algae have settled in the pond, then of course no preventive measures will help. Action must now be taken urgently, because as I said: filamentous algae grow extremely quickly and will soon take over the entire pond.
First of all, it makes sense to use the fishing net to fish out the thread algae, which are quite visible and more or less coherent. If you recognize the infestation at an early stage, you may be able to turn the corner and slow down the spread.
If the infestation is already advanced, algae killers may have to be used. However, they should only be used in emergencies and have no permanent effect. Algae killers clump the algae together, making them easier to remove from the water by a filter pump system. UVC lamps also have the same effect.