Learn All About Fish Pond Filters & Pond Water Quality Part1 of 4

In a pond toxic chemicals build up naturally ... the fish secrete these toxic chemicals like ammonia and unless they are removed by continuous bio filtration the fish will eventually poison themselves to death. Sand filters as used in swimming pools are bad for garden ponds

One of the most fascinating parts of pond keeping for the enthusiast is the management of the pond water quality. Highest quality water is probably the most sought after objective. If the water quality is good everything else falls into place. This is the purpose of biofiltration. Note we talk of BIOFILTRATION and not just filtration. There are significant differences and a basic understanding of the difference is important.

Clear water alone is no indication of the quality of the water.

In a swimming pool water is normally pumped through a sand filter using a strong pump that can develop enough pressure to push the water through the fine bed of sand. In passing through this fine bed of sand any solids are removed by trapping. Thus such a filter does the job of removing solids and particles that remain suspended in the water. If there is an automatic pool cleaner the sand filter also removes those solids that settle on the bottom

This is classical filtration namely the removal of solids from liquids.

However the filter in a swimming pool does not purify or clean the water. This job is done by the use of chlorine-based chemicals or chlorine generating devices such as salt electrolysers. In this way the water remains perfectly safe to swim in because the chlorine kills all the harmful bacteria and sanitises the water. Lots and lots of potentially harmful bacteria would otherwise build up in a swimming pool and many of these would come from inside the filter itself now you know why public swimming baths smell so highly of chlorine type chemicals.

Sand filters are used extensively on swimming pools.

Just think a moment about your sand filter if you have one. If you could see inside and watch exactly how the water flows through the bed of sand you would notice that many areas never see fresh water because they are partially blocked by accumulated debris that had never been able to be cleared by backwashing.

You would see that the water flow is through channels rather than across the whole surface of the sand bed. As such stagnant areas develop and in these areas bacteria of the undesirable kind also develop (mainly anaerobic bacteria . ie those that do not need oxygen) survive and multiply. Since chlorine kills all bacteria that find their way into the circulating water this situation is not serious in a swimming pool.

In a pond toxic chemicals build up naturally ... the fish secrete these toxic chemicals like ammonia and unless they are removed by continuous bio filtration the fish will eventually poison themselves to death. Sand filters as used in swimming pools are bad for garden ponds

Consider what happens in a pond where obviously no chlorine can be used because it would immediately kill any life in the pond.

Food is thrown into the water, some of which is eaten and the rest remains behind. That which is eaten by the fish is partly digested and partly expressed as a waste product, which sinks to the bottom of the pond. The fish needs to urinate and this passes into the water also. Fish also express impurities (nitrogen based chemicals) from their system out of their gills. In addition other animals enter into and out of the water and on windy days anything can find its way into a pond.

Here is an ideal opportunity for pathogenic bacteria to develop and toxic chemicals to build up.This is exactly what happens, all day every day!

If there were no means of purifying the water the fish would quickly poison themselves. Every kid has had a goldfish bowl and cried when a week or two later the goldfish suddenly died. The poor fish poisoned itself to death no doubt helped by the overfeeding to be kind.

In nature all sorts of factors combine to keep natural waterways healthy. In a pond however things are different. There are too many fish for the volume of water, the fish are overfed, there are few natural surfaces and plants to help clarify and purify the water.

To overcome these disadvantages biofilters (pond filters) are used.

At their simplest these biofilters (pond filters) are literally black or green boxes square or round, fat and thin or whatever. Often they hold sponges, brushes or other means of trapping solid particles. The boxes also contain plastic tubing often called Flocor, plastic balls, other weird plastic shapes, lava rock, special tape, string bags and coke bottle tops. If you are lucky the boxes contain Alfagrog. The collective name for these objects is biomedia ie a medium (better still surface) on which biological activity can take place

Next pond filter chapter

"The Complete Pond Solver" by Tony Roocroft  Essential reading for anybody who wants or has a garden pond. Get 12 Excel pond calculators free as well as "Water Lilies and Pond Aquatics" ebook also free. THis page is an extract form this book