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.
The 3 most popular mechanical sieves on the market are the Cetus sieve, the Compact sieve and the ultra sieve. Each one does exactly the same job as each other however do have varying differences in design, screen mesh size, pond capacity, suitability of your existing system and of course price. We have produced the details of each of these three popular models direct from each manufacturer so you can understand each models abilities and suitability to your system or new pond build.
The Cetus Sieve
The Cetus sieve is a totally new, bow screen pre-filter, made using the latest rotational molding technology. With all of its benefits and build quality, The Cetus sieve is undoubtedly the best of its kind on the market today, regarding quality and performance! The Cetus sieve is designed to efficiently and effectively 
remove large amounts of mechanical waste from a pond. The Cetus sieve can be set-up gravity OR pump fed and has many benefits over the original bow screen technology.
This Cetus sieve has a variable inlet height using the unique patented Pondflow regulation system – for use when gravity fed. This allows water levels within the pond to drop without causing the circulating pump to be starved of water. The Cetus sieve will allow a skimmer or a bottom drain to accept vast amounts of waste without excessive cleaning needed to be carried out. The water must then be pumped to either a normal filter above pond level (Nexus Eazy/Eazy Pod) or to a pressurised filter.
If pump fed, The Cetus sieve is placed above pond water level and then the exit water is gravity dropped into your main filter.
It is advised that all pressurised filters be pre-filtered using a Cetus sieve to reduce excessive backwashing and maintenance due to heavy solids.
* The Cetus sieve can be gravity OR pump fed
* Perfect fit screen so no waste can bypass
* Totally reliable and simple to install
* Plug and Play – comes with flexible boots to connect to pipe work
* Greatly reduced backwashing / maintenance of pressurised filters
* Robust one piece mould –no welded joints – no leaks!
* Large waste collection area which slopes to sump outlet
* The Cetus sieve is ideal for mechanically filtering skimmer lines
* Patented float that gives constant flow for gravity-fed level fluctuations
* The Cetus sieve has a maximum flow rate 18,000 litres per hour
* Tri-slot 300 micron wedge wire screen in 316L stainless steel on 100% of surface area
* Increased levels of oxygen
The Compact Sieve
The compact Sieve is a pump fed System and gravity return to pond, this unit can be used as a pre filter for ponds or can be used with a pond skimmer.
Product Specifications:
Stainless steel sieve: 24.5cm wide, 40cm long, and has slots of 250 micron. Pumping speed up to a max of 2000 gallons p/h. Output and overflow are 75mm 
push fittings.
External Dimensions:
Length: 50cm, Width: 33cm and Height: 56cm.
The Compact sieve can be used for primary mechanical waste removal. Such as;
* A particle remover directly next to the pond or to a waterfall/stream return to the pond.
* A mechanical particle waste pre-filter before surface mounted biological stages.
* This unit can be connected to an existing pumped pond skimmer system. The unit must be mounted above pond water level.
* This unit could be connected to a pond vacuum cleaner and the returned water from the vacuum cleaner can be fed into the input hose tail via a T-piece or directly. For extra particle removal and saving your precious matured pond water.
This New Compact Sieve is ideal for the smaller ponds - great for ponds of up to 4,000 gallons.
The Ultrasieve III ( models I and II differ )
The Ultrasieve III is the most compact, gravity fed, sieve filter with the highest pump capacity on the koi market.
For years the Ultrasieve III has been leading and most reliable pre-filter for professional koi ponds. The Ultrasieve III is supplied with an extra large waste outlet, including a slide valve 110mm. 
A few years after the introduction of the successful Ultrasieve II it has been superceded by the Ultrasieve III. Most important features of the Ultrasieve III are the improved flow regulation and the new waste outlet which have fine tuned the overall performance. The total size of the Ultrasieve III is now more compact so it takes up less space.
How the Ultrasieve III works: Pond water will flow over the top of the auto-adjustable dam. This dam is connected to the float so its height is automatically adjusted. This system will ensure that the exact amount of water that is pumped out the filter will enter the filter on the inlet. Underneath the screen the Ultrasieve III comes with a pump connection of a 2" male threaded adaptor. The waste outlet on the Ultrasieve III is fitted with a 110mm slide valve.
Ultrasieve III features;
*Twin inlets (110mm)
*Multiple inlets possible
*Strong polypropylene house
*Max. flow of 30,000 litres/hour
*Extra large waste outlet, includes a 110mm slide valve
*Very compact (L x W x H) 65 x 37 x 99 cm
*Screen 200 or 300 micron
*Optional lid available
*Pump outlet 2" male threaded, includes 63mm/2" solvent fitting
As you can see from just the three models listed above, there are many varients and features to each model. These mechanical sieves are not cheap either, costing anything from £200 to £650 per unit which add that to the cost of your main filter it becomes clear why a vortex is still a very popular option to many many fish keepers.
