Once you know the volume of water in your pond you can start to consider your options. A word of caution here! Please be aware that a US gallon is 3.7854 liters, whereas an Imperial gallon (UK gallon) is 4.54609 liters. This issue may need to be considered when you are looking at product specifications for imported products.

What Are The Most Common Pond Filter Types?

* Pressurized pond filters have over the last 10 years or so started to dominate the pond keeping market, particularly in the small to medium sized pond category, which is the category the vast majority of pond keepers fall into. The reason for the success is due to: their outstanding reliability; the compact, space saving design; the pressurized operation that allows the filter to be placed away from the pond, out of sight and the fact that the water leaving the filter is still under pressure which means that it can be used to supply a water feature or waterfall. Another major advantage is the inbuilt back flushing system which allows waste matter to be expelled from the filter, simply by pressing a button or turning a handle. This makes routine cleaning easier. The three best choices in my opinion are the Fishmate Powerclenz pressurized filter range, Hozelock Bioforce range and the Oase Filtoclear models. All three brands are supplied with excellent warranties (5 years with Oase) and have been engineered to keep running costs to a minimum. If you are looking to prevent green pond water then look at the integrated UV clarifier models.

* A gravity return filter, also known as a gravity discharge filter is probably what the vast majority of us think a pond filter looks like, if we were asked to describe one. These rectangular box type filters are still extremely popular, throughout the world, despite loosing some of their market share to the pressurized pond filter variety, over the last decade. The major advantages of this type of pond filtration system are the low initial purchase cost, the ease of installation, the availability of different models and because the design has been around for so long, most of the kinks have been ironed out. This submersible pump fed system relies on a pond pump to power pond water to the filter, where it is purified of debris and ammonia before flowing back into the pond under the influence of gravity. For this reason it needs to be positioned at the highest point of the pond. I would recommend the Fishmate gravity return filter because it is supplied as standard with Supra bio media (Alfagrog in the UK). This low cost filter media encourages large colonies of ammonia oxidizing bacteria to colonize, ensuring that ammonia is removed from the pond water quicker than it would be if plastic coils or lava rocks were used.

* Fluidized bed filters, more commonly known as bead filters are professional pond filtration systems aimed at pond owners with large ponds and large fish loads, particularly Koi. The secret to the effectiveness of a bead biofilter is the design; the biological chamber is home to upwards of 500,000 tiny beads that are suspended in water in a pressurized environment. The violent thrashing together of fresh water, oxygen, beads and ammonia (NH3) provides the best possible scenario for quickly and efficiently breaking down ammonia. There are some disadvantages however; they can be very expensive to purchase; the beads will after a period of time clump together in what is known as channeling. This reduces the effectiveness of the beads in oxidizing ammonia and will require a back flush to break up the solid mass of beads and pond waste. Occasionally some of the tiny beads break and become lodged in the internal laterals of the filter unit. In the USA the leading bead filter is the Aqua Ultima range by Aqua Ultraviolet. Other popular models are the Aquadyne range by Koi Camp Aquariology, the Aquabead and Biotek range by Grand Champion Technologies (GC Tek) and the Challenger and Econobead filters by Fluidart Technologies. Some of the models are supplied with a lifetime warranty.

* A gravity fed pond filter needs to be installed adjacent to the pond, and at the same level. Pond water is fed into the system via a bottom drain. This multi chamber filter incorporates a pump in the final chamber that forces water back into the pond under pressure, often via a venturi. As a result the pond surface will always be slightly higher than that in the filter, causing water to pass through to the filter via the bottom drain under gravity. This type of bio filter is tricky to install and is usually used in large Koi ponds. A vortex Koi filter is an example of such a system and is the preferred filtration system in the UK and in Japan, the ancestral home of Koi. The major advantage of a vortex filter is that waste matter is not able to come into contact with the nitrifying bacteria. This helps to ensure better pond water quality and less opportunity for heterotrophic bacteria to pollute the pond and cause fish diseases.

What Factors Affect Pond Filter Choice?

The choice of pond filter type is dependent in the most part upon the volume of water in your pond and the number and type of fish stocked. As a rule of thumb if you have a pond up to 1000 US gallons I would recommend either a gravity discharge filter or a pressurized pond filter, as the larger Koi pond filter systems would be far to expensive for your needs and would also be over kill. These larger Koi pond filters are better suited to use in large Koi ponds where there are large volumes of water, ammonia and solid waste matter. When looking at a particular brand, take a look at the manufacturers website where you will often be able to find downloadable user guides and installation manuals.

Retailers will often advertise big filter models for big ponds and smaller models for smaller ponds. On the whole this is a marketing ploy as it is not the size of the filter that influences its effectiveness! It is the size of the bacteria colony available to break down ammonia, along with the availability of oxygenated water allowed to mix with the bacteria. Remember that the single best way to improve biological pond filtration in gravity discharge filters and pressurized filters is to use a filter media with a high surface area, as this allows more nitrifying bacteria to colonize. It is a numbers game! The more bacteria available, the quicker ammonia will be broken down. In addition a biomedia with a higher surface area means that you will need less of it, which means that you physically need a smaller filter in which to store it. Supra pond filter media is an excellent low cost, porous product with a high surface area.