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a clear chemical-free pond?

Updated: Aug 1, 2018

Our Pond.


About ten years ago we built a pond in the garden of La Tierra. It measures about 10 x 4 meters. The challenge from the very beginning was to keep the water clean as if it were a natural pond in spite of the high temperatures in summer in southern Spain. In a natural pond there is no liner and therefore there is a direct connection with the biology in the soil. Unfortunately in dry grounds you need a liner which means one cleaning mechanism less to count on. By separating the water in the pond from the soil we have to make our other mechanisms larger and/or more effective.

The two main mechanisms that we have are plants and surface (for the microorganisms to adhere to).


Algae are a nuisance but can only thrive if there are sufficient nutrients in the water. The right plants in the pond (‘planted’ not in soil but in little stones or pebbles) are the ones that take away as many nutrients as possible before the algae can kick in.

A part of the pond (at least 50% of the pond’s surface) should be shallow (about 30-40 cms deep) for these plants. Plants don’t need to be fertilised, they will live off the nutrients that the microorganisms produce when they clean the water.

Some goldfish or koi are possible, they will add natural fertiliser and eat the mosquito larvae.


Microorganisms need sufficient surface to adhere to. Rocks, lava stone and other objects are to be placed in the pond for the microorganisms to grow on. The more surface you create the more “volunteers” you will have.

Frogs eat mosquitos, the watersnakes (Natrix Maura) wil eat the frogs, etc.

Other measures

The correct design of your pond is essential. A shallow area for the plants is vital. Another area (about 80 cm deep) could be planted with lilies. Apart from being beautiful when they flower, they provide shade, keep the water cool and serve as a hammock for the frogs.

A deep area is also important: leaves and branches that fall into the water will pile up at the bottom and slowly decompose. You don’t want to disturb that area or clean it too often. It is a anaerobic process and smelly, but a very natural thing that also occurs in natural pools. Leave it alone and it won’t bother you.

Some circulation in the pond is always beneficial. Solar powered pumps are particularly suited for this and help create the lovely sound of falling water.

A pond adds significant biodiversity value to your garden. In general, the more biodiversity, the better. The pond will attract birds and small mammals to come to drink. The birds in turn eat the insects and the frogs eat the mosquito larvae. Too many tadpoles? Biodiversity will take care of the balance. Our responsibility is to design the pond in such a way that is doesn’t need our interference. If it does, we need to adjust the design.

Sitting by the pond and observing life with all the coming and going of dragonflies, birds, frogs, (innocuous) snakes and boatmen and other insects has got to be the best way to enjoy your garden. Gratitude is felt by everyone and everything present.

You can contact me for further details, advice or for the design of your future pond.

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