Koi Ponds Goldfish Ponds Filters & Pond Solids

Page Summary: In South Africa where I live many koi pond keepers install sand filters to "polish" the fish pond water. Whilst I frown upon the use of sandfilters in a pond environment the sand filter is a great example of a mechanical filter installed to remove solids in the circulating water. The sand in the sand filter is very small and forms a dense bed through which its almost impossible for any normal debris to pass (not so for algae). The sand filter used to remove very fine particles must not be confused with a pond biofilter which is installed in order to purify the water (hence the name mechanical filter). It is not the prime function of a biofilter to remove solids. Most solids settle to the bottom of the pond anyway and need a vacuum to remove unless a bottom drain is installed in the koi pond.

Mechanical water filters for koi ponds

Even though we use clean, potable water to fill all our garden ponds that we are going to stock with koi, goldfish or other pond fish, water quality is an issue that must remain at the top of any koi keeper's priorities.

Normally we use tap water that has been purified by the local council or municipality to fill ponds. This is, of course, exactly the same water that we use in our homes, to drink, wash with and to water the garden. The reason they purify water is because it often contains pathogens, including viruses and bacteria which can make us sick.

Before water is purified, it also contains other impurities including unwanted minerals and particles of sand or silt.

Some water contains a lot of limestone; some contains lots of iron. Generally the local authority will add chlorine, possibly fluoride, and any other additives they have decided will make the water safer and more palatable for human consumption.

This doesn't, however, mean it is the best water for our fish.

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Purifying water to clean it

Mechanical pond filters and the water purifiers used to cleanse our municipal water are similar in terms of how they work. Both rely on various media – including foam, mesh, screens or gravel – to literally sieve out dirt, waste and algae. Of course the process followed in the purification plant is a lot more complicated. First the water is screened; then it is treated with chemicals, before it is channelled into various tanks where impurities separate out of the water.

Because chemicals are added to the water during the purification process (to get rid of unwanted dirt particles), additional chemicals must be added to balance the water. For instance, aluminium sulphate is used to control the muddiness or turbidity of water. Sodium silicate and calcium hydroxide (which is slaked lime) is used to neutralise electric charges in the water and force the particles to coagulate. Sulphuric acid and slaked lime is added to hard water with a high mineral content. This makes it more alkaline, but the lime makes it feel and taste distinctly soapy. So carbon dioxide is bubbled through the water to improve its feel and taste. At this stage the water will look clean, but there is no guarantee it is pure and potable. So the water is then filtered, usually through huge sand filters where the impurities and bacteria are trapped in the sand. Finally it is chlorinated to disinfect the water and kill anything harmful that might have got left behind in the water.

Chlorine is a pale green-yellow gas that is toxic if not used correctly. Even though it is commonly used to purify water supplies worldwide, and to maintain the cleanliness of swimming pool water, chlorine is a controversial additive and one that most koi keepers are wary of. This is one of the main reasons that pond water purifiers have been designed to act long-term on a molecular level, further balancing tap water (or borehole water if this has been used).

The filters used to purify koi pond water

While mechanical filters vary in design and how exactly they operate, this explanation will show generically how they work.

Typically a cartridge pre-filter will absorb minerals like iron. Even if you don't test the water to see if it contains iron, you will soon see the pre-filter turning a muddy red or brownish shade. Eventually the filter will need to be replaced. Then a carbon filter is used to further process the water. There are different types and grades of carbon, but generally carbon will get rid of organic material including unwanted chlorine, and any herbicides and pesticides that might have made their way into the water.

Ultimately a good mechanical filter will ensure that your koi and other pond fish have the best possible water that is available using this system of mechanical water purification.

Youll be amazed at how simple it can be to breed fish with the help of spawning brushes. Spawning BrushYoull need one mature female and at least two males.

Put the brushes one above the other at the edge of the pond. Spawning usually occurs in the early morning after a night of flurried activity and can take several hours. Most of the eggs will stick to the brushes which can then be taken out of the pond and put in filtered water of the same temperature. If the eggs are not separated from the adult fish they may be eaten.

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