Whether you own a garden puddle or extra large swimming pool for koi there are some things to consider when it comes to filtration. This article will not discuss which filter is best/worst but will hopefully help you narrow down your selection from the wide range of choices available, including creating one yourself.
1. What is being filtered?
Is this an all-in-one filter designed for Mechanical separation, biological nitrification, and chemical filtration? OR is this merely a single filtration unit in a system or group? You must determine the scope and size requirements of any filter you consider adding to your pond and assess its strengths and weaknesses within your system.
2. Is the filter designed for your pond or something else? Example: I once considered purchasing centrifugal separator filters that were designed for water purification. But upon further research I found they would clog with algae. Sometimes we pond owners also turn to pool industry products like bead filters. You must carefully research such items since their design assumes a low algae, high chlorine environment and so heavy dirt removal and nitrification are not really what they were designed for. We pond owners are often the targets of exaggerated claims by manufacturers too about the capacity of their products. Will that 12″x 10″ barrel with a 9 watt UV bulb really clean your 2000 gallon pond?
3. What is your budget? And more importantly what is the value of the pond and fish you are filtering? It is often said we are really water keepers rather than fish keepers so we could potentially spend more on the filters than the fish we keep. Some inexpensive to build DIY filters may perform as well as professionally produced products but may not be as attractive in the landscape.
4. For mechanical filtration – How small a particle are you trying to remove with the filter under consideration? Determine which types of filters are best suited for that particle size. If there is much debris in the pond from overhanging trees you will have more debris to remove than if the pond is indoors.
5. How often will you maintain the filter realistically? Maintenance can be easy or difficult to get the filter to like new condition. Also does the maintenance need to occur so regularly that you can not go on vacation?
6. Does the design of the filter allow for a thorough cleaning, or does backwashing leave a build up of potentially dangerous sludge. One fault that most equipment dealers will not point out is the amount of debris that remains in your filter during a normal cleaning. Bead filters may run clear during backwash but still contain a full inch of muck inside harboring bad bacteria. Other systems may seem clear after backwashing too, but until you remove the media you can not see the hidden dirt. Gravel bog filters are probably the best at trapping solids but are also the hardest to clean.
7. Can you see into the filter to determine when it needs to be cleaned? Many pond owners will allow their filters to run until they slow the water down due to sludge build up. It is important to regularly remove the K1, brushes, matting, or other components to insure the cleanliness of the filter.
8. How much water can flow through the filter when clean vs filthy? If your filter is a mat or sponge type it will slow water down as it fills with debris. It will also be less effective at both mechanical and biological filtration. Certain plastic media are designed not to slow water.
9. Does the filter have any moving parts and if so are they durable? Drum filters and Sieves with floating valves come to mind as filters with moving parts that can wear out, become dislodged, or fail for other reasons.
10. Is the size of the bio filter and it’s media adequate for your pond and its flow? How large it should be is a major issue for pond owners since there is no magic formula for all types of filters. If you regularly have ammonia and nitrite spikes your filter is not large enough for bio filtration. If your water is cloudy from fine particles, you do not have adequate mechanical filtration. You can not over filter a pond but usually must consider the aesthetics and placement of the filters for the garden area. This can lead to trade offs due to size and potentially inadequate filtration.
11. What is the filter made of and can it withstand the elements over time? Many are durable plastics or fiberglass and can last for years. Less expensive items may become brittle with time. Many of the DIY barrel filters and planter filters will need to be replaced every few years.
12. What Pipe sizes do the inlets/outlets support? Pipes and hoses to and from the pond are relatively inexpensive until you get to the 3-4 inch size. For Koi ponds a generally good filter design will use gravity fed from bottom drains to the filters then pump clean water back to the pond or other system components. A filter that only supports 1″ pipe isn’t likely adequate for a 4000 gallon pond and high pump flow.
13. Will the filter be pump fed or gravity fed? The hardest thing for me to grasp was the importance of a gravity fed system. The use of a bottom drain running to an external chamber will allow most of the debris that sinks to be carried away from the pond and dumped to waste. This debris is not chopped up by the pump and is thus easier to flush away. You can have just your mechanical filters gravity fed and then pump feed bio chambers if desired. For small water gardens where the pump is submerged in the pond you will have to clean your pump box regularly to keep the water flowing. well. Gravity fed systems have far more advantages than pump fed filters but require more planning during the initial build of the pond. Gravity fed units are usually at the same height as the water level in the pond.
14. Flow and Tracking – Filters are either upflow, downflow, or horizontal flow designs. Water will take the path of least resistance and will channel through the filter unless acted upon by another obstacle such as baffles, air bubbles, matting, or other media. The goal of any mechanical filter is to provide a barrier to dirt while allowing the flow of water. Bio filters should come in contact with all water passing through the filter to operate at maximum efficiency. Do note however that most bio filters have stagnant water areas which can lead to possible poor water conditions. Horizontal flow filters have the most efficiency for media contact and water can be easily disrupted with air bubbles or media in its path, which allows for maximum nitrification.
15. The magic box – There is no perfect filter for your pond regardless of what that nice salesman at the garden center tells you. The trick is to determine what size filtration you may need for your pond, check the water parameters regularly, then make adjustments to flow rates, aeration, UV power, and other system components that help your filter do its job. You may even need to change out that lovely overhanging tree to an evergreen to reduce the debris that falls into the pond. If you can talk to other pond owners and learn from their mistakes it will help you decide which filter is best for your pond and its inhabitants.
Do keep in mind that KOI ponds differ greatly in their filtration requirements than do goldfish ponds and water gardens. Buy the appropriate equipment for your pond and you will only have to pay for it once.