Articles For The SA Hardware & Gardening Retail Trade

Green murky ponds how to solve the problem and make extra profit too. Do you really want to make your pond keeper customer very happy?

One of the very best inventions that transformed pondkeeping was the ultra violet light. Despite having been around for many many years more than 90% of all people with a pond have never heard of it.

Every retailer involved in water gardening must have been confronted with the following statement from a potential customer My pond is green what can I do about it?

Often the reply will be Ah, you need a bio filter.

But you know what; this is the completely wrong answer.

Nevertheless the customer respects this expert advice and she buys a biofilter and guess what the pond stays green and murky.

What is a biofilter designed to do?

A biofilter is essential for a fish pond but its critically important function is to purify the pond water i.e. remove the toxic ammonia that builds up as a result of normal fish metabolic processes.

The biofilters secondary job is to help remove solids that may be getting into the pond from various sources wind, leaves, grass cuttings and food residues put out by the fish (those curly bits you see on bottom of the pond).

Why does a pond go murky and often green (sometimes brown)?

The cause is algae algae are tiny plants that thrive in warm water, high sunlight conditions and especially where there are fish. Fish are the source of the algaes food; nitrogen and phosphorous compounds.

Algae are far less of a problem in a pond where there are no fish.

Suspended alga are about 4 microns in diameter which means they are far too small to be removed in any filter I have ever seen and this includes a sand filter. Once this basic fact is appreciated then it becomes obvious that a biofilter can never be the solution to a suspended pond algae problem.

So what does Ultra Violet light do to solve the problem?

When pond water containing suspended algae is pumped through a UV unit the radiation from the UV lamp destroys the cell wall structure of the algae and these bits of algae debris then stick together and become much bigger than 4 microns. In this bigger state they are able to be removed in a biofilter or they just sink to bottom of the pond. The UV does not stop the algae forming and this point is important the UV power must be high enough to kill the algae almost as soon as it forms. If the unit is undersized the unit will still kill algae but they will form more quickly than they are being killed and thus the water will remain murky and green.

In the next article I will go into detail on how to specify and select the right sized UV unit.