If the pond is going to house more than one or two goldfish then filtration is essential.
The first rule of filters is the more the merrier as you can never have too much filtration! Filtration serves two functions, to filter the water both biologically and mechanically. A good filtration system will consist of 3 major products, the filter, a Ultraviolet Sterilisers (UV) and a pump to operate it.
There are 3 main types of filtration system available, combination, gravity returned and pressurised. Filters are available with or without Ultraviolet Sterilisers that keep the water crystal clear.
Having a UV will eliminate green water which will almost certainly develop if the pond is exposed to direct sunlight. A UV will also protect the pond from unwanted bacteria and parasites. Most modern filters designed to run ponds up to 48000 litres come with an integrated UV for ease of instillation and price efficiency. Filtration is entirely dependent on the size of the pond and the stock in it.
Volume is calculated by L x W x D = Cubic Feet X 6.24 = Gallons x 4.45 = L It is always recommended to over filtrate a pond as the filter will need cleaning less frequently and provide a better bacterial foundation for the pond while maintaining a more stable environment for the fish and wildlife.
Combination filters are designed for smaller ponds (under 1000litres) and include a pump that can be used for a waterfall or fountain and an attached filter. Normally the entire system is designed to be submerged underwater, so that nothing is visible from outside the pond.
Gravity returned filters are the most popular choice of filtration for koi enthusiasts and keepers of larger ponds. The system works by positioning the pump at the bottom of the pond and pumping water through pipe up into the filter box. The filter is situated above the pond level so that gravity pulls water through various media in the filter box and down a return pipe, possibly down a waterfall and back into the pond. Filter boxes are available with or without an integrated Ultraviolet steriliser in single and multi chamber variations. The more chambers a filter has the more media it can store and the better the filtration will be.
Pressurised filters are the newest edition to the filter family. The systems represent high performance low maintenance pond filters that operate under pressure. They are the most technologically advanced filters available and have revolutionised the way ponds are maintained and managed. All high end pressurised filters come complete with advanced backwash cleaning systems and integrated Ultraviolet sterilisers reducing complete filter cleaning down to just a turn of a dial and a couple of minutes of your time. Water can be pumped into the filter (by the pump sat on the pond bottom) and continue pumping upwards after it has left the filter. This allows for a neater instillation as the filter can be buried up to the lid and disguised well. Piping can be used to direct the water flow to the top of a waterfall or back into the pond.