Like most animals, fish excrete urine and produce solid waste (faeces), both of which are passed via the vent. The urine consists mainly of water with a small amount of urea; the main nitrogenous waste product from the breakdown of proteins is ammonia, and this is excreted through the gill membranes. Faeces are largely remnants of undigested food.
In the wild such waste products and their decomposition are diluted and/or removed by the relatively large volumes of water or the continuous flow of water as found in rivers and canals. In our ponds the breakdown of the waste products becomes the job of the filtration system, required to perform the cleansing role of the water that occurs naturally in lakes and reservoirs.
There are hundreds of various filters on the market for a various range of ponds, all of these filters take on the principle role of the water cleansing and the methods used can be divided into three main principles, Biological, Mechanical and Chemical filtration this section will cover these in detail for a better understanding of each.
The filtration of koi and sturgeon ponds is forever changing, every year manufacturers produce a new line of equipment to hopefully enable the pond keeper the best possibilities of keep their fish healthy and the water in which they live as pristine as possible. The most recent options to the fish keepers filtration systems are the variety of mechanical sieves on the market, each varying in its capabilities and suitability of an existing filtration system such as a pump fed system or a gravity fed system there is a mechanical sieve either dedicated to each or can be altered to suit.
What does a sieve do?
Simply explained a sieve does exactly the same as the one in any households kitchen cupboard. it removes any substance to large to fit through the mesh however when we look at a pond sieve the screen mesh used has holes measured in microns, far smaller than a household sieve as 1 micron is equal to 0.01 millimeters. There are a number of mechanical sieves on the market and size of the screen varies between manufacturer some even come with the option to change the size of the standard screen supplied. On average a screen size will be between 200 to 300 microns depending on model chosen. The three most popular sieves details can be found further down this page. So the whole point of a sieve is to filter out any material larger than the screen size from entering the main filter system. These mechanical sieves have become a key piece of equipment espically to those fish keepers using bead filters as they reduce maintainance time and cleaning of the whole filter system as the sieve removes almost all of the waste from the pond that would normally build up inside the main filter. Previosly many systems encorporated a vortex to do this job however as product manufacturers develop and design the sieve has become probebly the best line of mechanical filtration ever.
To start with make sure you have all the fittings required including the additional fittings to set up the filter to be pump fed ( pump in pond ). With the filter you should be provided with a 3 inch to 2 inch rubber boot and a slide valve these are fitted to the verticle water inlet pipe using the supplied jubilee clips.
From the slide valve you need to attach your pipe from the pump, this can be done using solvent weld pressure pipe or by using flexi pipe. First you will need a stepped hose tail (1.5 inch ) If you are using pressure pipe this is not required. Fit the hosetail inside the reducer ( 1.5 inch ), you may notice that the reducer has an internal lip so we advise cutting the stepped hosetail down to match your pipe size then glueing into the reducer. This stops anyone glueing the fittings into the slide valve the wrong way round, clean any excess glue with a damp cloth. 
