Pond shells in garden ponds: Natural water filters

 Pond shells are really good water filters under certain conditions. With these tips they will also become at home in your garden pond.

Pond shells in garden ponds: Natural water filters
iStock/VitalisG Pond shells can help to keep the water in the garden pond clear

pond shells are quite powerful water filters 

and under certain conditions they provide clear water in the garden pond. 

Most people only know mussels from the sea. 

But there are also native freshwater mussels that live in rivers 

or lakes and are also suitable for the garden pond. 

Among them are the Common Pond Mussel (Anodonta anatina), 

the much smaller Painter Mussel (Unio pictorum) 

or up to the Large Pond Mussel (Anodonta cygnea), 

which grows up to 25 centimeters in size. 

To reach this size, however, the mussels also need years.

Pond shells in a garden pond: What are the advantages?

Why should you put pond shells in your garden pond, 

which you will rarely or probably almost never see later? 

Quite simply: They are living bio-water filters and work 

like technical pond filters - dirty water in, clear water out. 

The only difference is that you don't have to clean filter 

sponges on a pond shell, because the permanently sucked 

in water stream supplies them with oxygen and food. 

The filter sponges do not need to be cleaned 

because the permanently sucked in water stream supplies them with oxygen and food. 

They aim for floating algae and so-called 

plankton in the pond - almost microscopically tiny water inhabitants. 

Pond mussels live on the bottom and dig themselves in easily. 

To make sure that enough floating particles pass by, 

the mussels help a little - with their foot. 

Even though this rather clumsy organ allows 

the pond mussels a certain freedom of movement, 

it is not meant to run around, 

but rather to dig into the pond floor 

and stir up sediment in order to fish plankton, 

algae and also dead material out of it.
Pond shells in garden ponds: Natural water filters
iStock/Kerrick Pond mussels feed on the microorganisms in the water

Pond Mussels are filter feeders and not algae-eating filters, 

they live on microorganisms in the water. 

Therefore, pond mussels are not a supplement to the classic filter system, 

but rather a support for the natural water purification in the natural pond. 

Because if the water is too clear and low in nutrients, 

the mussels simply starve to death, 

and of course you don't put them in the pond to do this.

Disadvantages of pond mussels in the garden pond

Do pond shells fit in every garden pond? Unfortunately no, 

a few requirements should already be fulfilled. 

They are not suitable for puristic concrete ponds, 

ponds with hardly any plants or mini ponds. 

This also applies to ponds with filter systems 

that simply take the food out of the water. 

Circulation pumps of a stream are usually unproblematic. 

The filter performance of pond mussels is not a constant 

parameter as with pond filters, but depends on the possible fish population, 

the pond size and of course on how sunny the pond is. 

Since pond mussels are not machines, 

their daily filter performance cannot be named in general 

and the required number of mussels per pond is not a purely mathematical value. 

Pond shells are not dangerous for other pond inhabitants. 

Large fish, however, can eat the mussels - depending on their size - or at least 

damage them or press them so hard that they no longer filter and starve. 

Dead mussels can in turn give the pond a poisonous 

protein shock for a short time and endanger the fish population.

Filter capacity and necessary number of pond shells

A pond shell filters a good 40 liters of pond water per day, 

some sources even call this an hourly output, 

which can be quite acceptable under ideal conditions. 

However, the filter performance is never constant. 

Since these quite sensitive animals adapt to changes 

in water temperature or other environmental conditions 
with their activity and thus also the filter performance, 

you should only start with a few pond mussels in 

your garden pond and wait for an improvement in water quality. 

If the water becomes clearer after one week, 

you will not need any more animals. If, on the other hand, 

the water is still cloudy, 

insert another pond shell and feel your way to the required number.

MSG/Patrick cock To be able to insert pond shells into a natural pond, the bottom must be sandy or fine gravel

How to keep pond mussels in a species-appropriate way

Since a pond mussel likes to dig itself two-thirds of the way 

into the water for protection and pre-filtration, 

the pond bottom must be sandy or at least fine-grained - at least 15 centimeters thick. 

The bottom should not be covered by a dense root network, 

the mussels hardly have a chance. 

Pond mussels must filter the water to stay alive. 

Therefore they need a certain volume of water to find new food. 

After all, you do not want to have to feed the pond mussels. 

You can roughly calculate with 1.000 liters of water per mussel, 

so that they can filter enough food. 

It depends on the quality of the water, 

it must not be too clean and possibly already processed by technical filters. 

Often mussels can manage with less water, 

but with more volume you are on the safe side. 

In natural ponds and other sufficiently planted garden ponds, 

pond mussels can replace the filters completely. 

The pond should be at least 80 centimeters deep 

so that it does not heat up too much in summer and 

also allows a certain natural movement of water that is not hindered by plants. 

The garden pond should not heat up over 25 degrees Celsius in summer. 

Place the mussels on the sandy bottom of the pond at a depth of a good 20 

centimeters in a place without plant growth. 

If you use several pond shells, 

place them around the edge of the pond so that the animals 

do not slurp all the water in their environment and the others do not get any.

How pond mussels get through the winter well

In autumn, the pond mussels go down one floor so that they 

do not freeze to death in the shallower garden pond: 

Place the mussels in a water-lily basket or a bucket with at least 

20 centimeters thick layer of sand to bury them in and 

let it down on a stable string to frost-proof depths of more than 80 centimeters. 

In winter, pond mussels are not particularly active, 

so the cuddly proximity in the bucket does not bother them in this case. 

A further, but somewhat more cumbersome possibility for 

hibernation is an aquarium with pond water and 20 centimeters of sand. 

As soon as the pond cools below ten degrees Celsius, the time has come. 

Set up the aquarium in a cool but bright place and avoid temperature fluctuations at all costs. 

So that the animals do not starve to death, 

you should store pond water in a rain barrel in autumn, 

for example, and carry out a partial water change every two weeks in winter.
Flora Press/Buiten-Beeld/Jelger Herder For reproduction pond mussels are dependent on bitterlings

Multiplication of pond mussels

The pond mussels will remain without offspring in most garden ponds. 

This is because they depend on bitterlings, 

the smallest native carp species, for reproduction. 

The larvae of the mussels live parasitically in the skin and gills of the fish, 

while the mussels in turn take up the embryos of the bitterlings. 

This is annoying for both parties, but does not cause major damage in nature. 

In small ponds, however, this can be annoying for the fish. 

If bitterlings live in the pond and the pond is large enough, 

you can expect mussel offspring. 

But you don't have to worry about male and female mussels, 

they will take care of that among themselves. 

Like many snails, pond mussels are hermaphrodites 

and decide for themselves who will take over which parent part.

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