The most important element of water management is filtration. Filtration refers to the removal or reduction of suspended and dissolved materials in the pond. This is accomplished in two major ways. The first is through mechanical filtration which removes suspended particulate matter and debris. The second type of filtration is biological which chemically reduces fish-harming compounds in the water

   Mechanical filtration can be used alone, however, it is most commonly used as a precursor for a biological filter Bio-filters contain media on which bacteria grows. The media also tends to clog easily without good mechanical filtration.

   One common way to reduce the amount of particulate matter before the bio-filter is the use of a settling chamber. The ideal settling chamber is that which has a cone shaped bottom. As water circulates in the cone, friction of the wall causes sediments to fall and collect in the center of the cone. Another effective form of settling chamber is a round sump tank. This will work basically the same as the cone, except there will not be a deeper section for the debris to collect. Therefore, a sump must be at least twice the size of a cone to do the same job. In both cone and sump settling chambers there is a valve or drain at the bottom which is opened periodically to remove the collected particles.

   Another common way to mechanically filter water is with the use of a prefilter. Prefilters come in a variety of designs. Two basic designs are vertical down flow and horizontal flow. In both designs. water flows through filter material that physically removes the suspended particles. Some of the materials which can be used for filter needs are made out of foam or sponge and mattresses of bonded fibers. These materials are used in varying thicknesses up to 2 inches. Another kind of prefilter is one that uses filter brushes which also physically remove suspended particles. This kind of setup is usually arranged in a horizontal flow with the brushes hanging vertically, side by side. These brushes come in different sizes from 2 to 6 inches in diameter and 8 to 20 inches in length.

   All of the prefilters which I just mentioned will also support a colony of bacteria and carry out biological filtration. However, you can not have your prefilter double as a bio-filter. You must decide between the two. The reason why is that prefilters filter out solid particles, therefore they must be cleaned often. Bio-fliters support a colony of bacteria and cannot be cleaned without killing or washing out the bacteria.There is a mechanical filtration that I would like to talk about. This is the high rate sand filter. I personally do not recommend their use for two reasons. The first being the need for a large pump which also carries a big appetite for electricity. The second reason is that pressurized filters require constant back flushing and every time this is done you lose a considerable amount of water which will need to be replaced. The new water that you have introduced will throw off the balance of the pond.

   No matter which kind of mechanical fiiter you choose there is one last thing to take into consideration. To achieve maximum result, you should gravity feed into your mechanical filter and then pump to your bio-filter or pond. If the pump is located before the mechanical filter it will grind up all the solid particles into even finer particles. This will make it much harder for them to be filtered out of the water. I would like to stress the point that good mechanical filtration is a must. Without it, your filter will become plugged up and channeling will occur. Once this happens the filter will start to reverse the bio-filter process. Nitrates will be converted into nitrites and nitrites will be converted into ammonia.

  FILTRATION 101 (con'd)
by Jeff Eberle
From the NFKPC August 1993 Newsletter

  Before I start to talk about biological filtration I would like to re-state how important it is to have good mechanical filtration. Without a good mechanical filter before your bio-filter, the filter rnedia will become clogged with particles and the water will channel through it. Channeling has two adverse effects. The first is that the channeled water flows too fast to be chemically reduced by the bacteria. The second is that in the clogged regions of media some anaerobic bacteria will build up and will convert nitrates to nitrites and nitrites to ammonia. This reversal of the bio-filtering process can be detrimental to the fish. The only solution once channeling has occurred is to clean the filter media which usually results in great losses of bacteria. Again, good mechanical filtration is a rnust!!!

   The purpose of a bio-filter is to provide a place in the pond system where a colony of nitrifying bacteria can grow. These nitrifying bacteria convert ammonia to nitrites and nitrites to nitrates. The first condition that must exist for the growth of these bacteria is the presence of ammonia in the water. If the water is changed too frequently before the filter becomes established, it will only slow the build-up of the bacteria colony. One of the things that I recommend to help speed the start-up time of the of commercially prepared bacteria. This will help to "seed" the bio-filter with the nitrifying bacteria it needs to function properly.

   One of the reasons why many bio-filters do not function properly is because of inadequate aeration. The bacteria in the filter requires oxygen to carry out the reduction of nitrogenous wastes in the pond. If the water is not properly aerated between stages of the filter, the bacteria will only survive in the initial stage of the filtration process. The bacteria in the latter stage of the process will be few due to an oxygen depletion in that area. It is very important to oxygenate water before, during , and after its travel through the bio-filter.

   The biological filtration process releases hydrogen ions into the water which basically means that it produces acid. This has a tendency to lower the pH of the pond. To counteract this, I recommend the periodic addition of baking soda and/or the use of water changes. The amount of baking soda and the amount of water changes will vary depending on the stocking conditions, feeding levels, size of the pond, and many other factors. Start off small and experiment to see what works best for you. Remember--too little is better than too much! Go easy at first because drastic changes cause stress for the fish.

   A very important consideration with biological filtration is water temperature. If the water temperature drops, filter bacteria become less active thus removing less wastes from the pond. You should monitor your water conditions often if the pond water drops in temperature. The other time when temperature plays a major role in filter activity is in the spring when pond keepers are anxious to reclaim their living jewels from a long winter's nap. Remember to give the bacteria time to multiply and to become reestablished (this can take quite a bit of time in cooler temperatures). In the spring, feed the filter not the fish. Once the water starts to warm up, it won't take that long before everything is back to normal.

   In regards to biological filtration, I cannot emphasize enough the need for very close monitoring of water chemistry. Ammonia, nitrates, and pH should be tested occasionally. As I've stated in previous articles, the most important aspect of successful koi keeping is water quality. Hopefully, with the help of a properly designed and adequately sized bio-filter, you will be able to maintain good water quality and healthy koi