Pond Filters Selection Guide

What is a 'Pressurised' Pond Filter?

A pressurised filter is a 'canister' containing filter media and sponges. The canister is sealed and can therefore be pressurised, meaning water can be forced through the filter and then forced up hill by the pump, if desired.

Benefits & Disadvantages - Pressurised Filters.

Benefits:

• A pressurised filter can be buried at ground level, allowing the filter to be easily disguised. The filter inlet (from the pump) and the filter outlet should always be set above water level, so that the the water doesn't drain backward throught the filter, should the pump be switched off (or the dirt will flush back into the pond!). We supply a Rock Cover suitable for all Filtoclear Filters, which can be used to disguise the filter lid if desired.
   
• As the filter is pressurised, the water can be pushed up hill, perhaps to a waterfall, cascading water blade, watercourse or stream. The water being passed up to the stream has already passed through the filter, so this will be nice and clean.
   
• A pressurised filter can be fitted anywhere on dry land, between the pump outlet hose and the discharge point, making it easier to position the filter in a less conspicuous location (perhaps a flower border or at the top of a stream).
   
• Pressurised filters can be fitted with flexible hose on both the inlet and outlet side of the filter. This allows the pipework to be laid easily without the need for rigid pipe. If the flexible hose is to be buried below ground, we suggest using our Heavy Duty Flexible Hose.
   
• Pressure filters such as the Oase Filtoclear are fitted with an integral UVC (Ultra-Violet Clarifier).

Disadvantages:

• Pressurised Filter Systems rely on water being forced to, through, and out of the filter (and possbly up to a higher point). By the very nature of this system, the pump required to combat the additional pressure is likely to be more powerful than a gravity filter would require. On this basis, the power consumption would be greater than a Gravity Filter system.
   
• Pressure Filters are generally suited to smaller ponds (up to around 36000 Litres without fish). However, it is possible to use multiple pressure filters to service a larger pond, although this make work out more expensive on running costs and initial purchase costs, over a Gravity Filter System.

What is a 'Gravity' Pond Filter?

A Gravity Filter is usually in the shape of a box, and relies on a pump to force water into the filter box. The water then returns back to the pond using gravity (i.e. the cleaned water flows out of the box in a downhill run). The Filter outlet MUST be above the top of the pond water surface, otherwise the filter box will flood.

Benefits & Disadvantages - Gravity Filters.

Benefits:

• A gravity filter only needs the pump to pass the water into the box. The pump required to perform this task can therefore be less powerful than a similar pressure filter, so running costs are often substantially less. Bear in mind that a filter should be left running 24 hours per day, 7 days a week, so running costs are an important factor to consider.
   
• Gravity filters have a very large filtration surface area so require less frequent cleaning that a similar pressurised filter.
   
• Oase Gravity Filters are very easy to clean (for example, the Oase Biosmart Filter Sets , Oase BioSys Screenmatic Sets, Oase Proficlear).
   
• The Oase Filtomatic Gravity Filter Sets are self-cleaning, providing a virtually maintenance-free filter system.

Disadvantages:

• The outlet pipe must always be above water level (on dry land) so that the clean water can return via gravity. This usually means the filter box is physically above ground level, making this harder to disguise from view.
   
• Gravity filter outlet pipes are rigid plastic pipes and bends - not flexible hoses. See Biotec Discharge Pipes & Elbows department.
   
• A gravity filter cannot push water uphill after the outlet. If you intend to use the clean outflowing water to provide a stream, then the Gravity filter needs to be positioned at the highest point of the stream (so that the water can begin flowing downhill after the water exits the filter box).

Questions & Answers - Filters & Filter Systems. 

What is the difference between a 'Filter' and a 'Filter Set'?

Filter Sets contain the 3 most important components; a Filter Pump (solids handling pump), UV Clarifier and a Mechanical/Biological Filter. It is also possible to purchase the Filter on its own if desired, assuming you already have a suitable Pump and UVC.
 

Why do I need a UV Clarifier and what does it do?

An Ultraviolet Clarifier is a very important piece of equipment, if your pond is outdoors and open to daylight/sunlight. A UVC is essentially an ultraviolet bulb mounted in a special housing.

The pond water is pumped through this housing and the UV radiation will kill pathogens (harmful agents that can cause disease) and flocculate ('clump' together) single-celled algae (the cause of green water in a pond). The flocculated algae is then big enough to be trapped by the filter sponges, gradually removing this problem before it spirals out of control. The algae inside the filter is then broken down by the 'friendly' micro-organisms in the filter.