Koi Pond Filters
Pond Filters are at the heart of a good Koi pond system, they are the reason for having a filter, how the pond works, and how the filter will create a more liveable environment for our Koi are processes not easily understood by beginners. Indeed, even some older hands remain baffled about the more subtle aspects of filtration. It is simpler if you have moved from tropical fishkeeping to Koi keeping, as then you will, hopefully, understand the nitrogen cycle. That is one big step, but crossing the hurdle of tropical requirements to those of Koi is sometimes more of a quantum leap than some of us like to readily admit.
Is a question often asked at the beginning, so that is more than likely the best place to make a start. Pond filters are employed to remove ammonia from the pond water and not specifically to keep it clear. You can have an efficient filter that does not give you clear water in your Koi pond, although it must be said that the two do normally go hand-in-hand. Koi excrete ammonia directly from their gills as the disposal of part of their nitrogenous waste. Ammonia also comes from the breakdown of plant waste, of solid and liquid waste from the Koi, and the breakdown of all manners of other organic debris in the pond. In the enclosed pond environment, ammonia will accumulate and build up to toxic levels for the Koi. To prevent damage to, or at worst the death of Koi, this ammonia must be removed from the water. This is carried out biologically through the provision of a suitable pond filter. Pond Filters are at the heart of a good Koi pond system, they are the reason for having a filter, how the pond works, and how the filter will create a more liveable environment for our Koi are processes not easily understood by beginners. Indeed, even some older hands remain baffled about the more subtle aspects of filtration. It is simpler if you have moved from tropical fishkeeping to Koi keeping, as then you will, hopefully, understand the nitrogen cycle. That is one big step, but crossing the hurdle of tropical requirements to those of Koi is sometimes more of a quantum leap than some of us like to readily admit.
In a biological filter, ammonia is broken down by naturally occurring bacteria, firstly to nitrite, which is also poisonous to Koi, and ultimately to nitrate. In the quantities we can expect it, nitrate is not directly poisonous to Koi, although it can be a cause of blanket weed. Nitrate can be removed by other means such as a vegetable filter, or a denitrifying filter that employs different bacteria to convert it to gaseous nitrogen and release it to atmosphere. This biological process is referred to as "The Nitrogen Cycle". In reality, the Nitrogen Cycle works throughout the pond, not in the filter alone. All surfaces will support the necessary nitrifying bacteria. A filter, with the provision of large amounts of medium for bacteria to grow upon, ensures that enough biological action takes place to cope with the ammonia produced by the Koi. The 'biomass' (the bacterial colony) will establish itself to the load imposed upon it therefore it is keyed to the stocking level of fish living in the system.
Gravity feeding, looking at a typical Koi pond filter system it is generally accepted that for the best efficiency the water must be gravity fed around the system to enable settlement, where solid matter is separated from the water, to take place. In a gravity fed system the filter is usually mounted with its water level at the same level as that of the pond. It will have large diameter inflows, and the pump/s will be situated at the end of the system where they take water from the filter, and return it to the pond. The water in the filter is replenished from the pond under gravitational force - hence the name of the filter. Sometimes it is not practical for one reason or another to gravity feed a filter system. Then it will be necessary to use a pump fed filter system. Here the pump is situated in the pond (submersible type) and it pumps water into the filter. It is very important here to have free flowing medium, and a water bypass system fitted. This is because pumps when situated in the pond tend to liquidise the solid debris thus making it very hard to separate it from the water using settlement. The resultant high debris load in the water can cause filter blockage and overflow - hence the by-pass. Having read all of the foregoing, it can be seen that a filter is quite a complex part of the Koi pond system, and must be regarded as a living component, just as the Koi are. It should have equal care taken of it.
Already mentioned are flushes, which must be operated on a regular basis to keep the system clear of sludge. No matter how good your settlement is, this always seems to build up to a certain extent. You must take care also that no part of the filter system is cleaned with tap water as this contains chlorine that will cause nitrifying bacteria to die back. If you do have any parts of the filter system that do need to be washed, such as sponges, then do this with pond water and don't get things too clean. Washing off the worst of the dirt is all that is necessary. Your pond filter must never be switched off, apart from the odd half hour for essential maintenance, otherwise the nitrifying bacteria, starved of oxygenated water will again die back giving you a less efficient filter when switched on again. Likewise UVCs (Ultra Violet clarifiers) must never be switched off, apart from when medication of any sort is in the pond, although this statement could be seen as controversial in some circles. If you switch off UVCs for more than a short period, then you will get a build up of slime on the surface of the quartz tube that will reduce its efficiency when switched on again. The unit will then have to be dismantled to clean it with all the associated dangers of breaking the quartz tube. UV filament lamps should also be changed once per season as the emission deteriorates after a while.
Water testing is perhaps the most important part of Koi keeping as this can tell you a lot about whether or not your pond filter is working at peak efficiency. You should monitor firstly ammonia, and the presence or not of this will confirm for you whether or not your filter is performing satisfactorily, or whether it's efficiency is falling due to causes that need urgent investigation. You should then monitor nitrite (don't confuse this with nitrate), as nitrite appears after the first stage in the oxidation of ammonia. You can have the situation where there is no ammonia, yet nitrite persists, and this should lead you once again to investigate the filter performance. The third parameter of importance is pH. This can tell you a lot of things about your pond, and there is a certain band, which is better, suited to Koi. PH 7.5 to pH 8.3 is absolutely ideal, but Koi can exist from pH 7.0 to pH 8.5 without harm as long as it is stable. Any reading outside this range should be investigated and rectified without delay, but we would not advise that you tried any alteration of pH by artificial means such as the widely sold "pH buffers". Not only would this require a lot of buffering agent, but it would not be a permanent correction, would need to be repeated often, and you could thereby be masking a filtration defect, and then you will, hopefully, understand the nitrogen cycle. That is one big step, but crossing the hurdle of tropical requirements