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It looks as though I have been enlisted to design, help fabricate, and install a filter for a medium sized koi pond with fountain for a local church. It consists of a 16 foot diameter lower basin that hold 3000 gallons or so that has a 6' basin above it. It also has a large statue on top of the upper basin with a water feature. It is rather impressive and was fabricated and shipped here from China. They already have a decent sized pump hooked up to it to circulate water and run the fountain part of it, but they have no filter. The koi in it don't seem to mind and are doing extremely well, but they are difficult to see except at feeding time. That will soon change. If money was no object and a large pressurized sand filter or media filter was easy to procure here I would go that route, but their budget along with water and electricity concerns have caused me to formulate a better route which is as follows: The upper basin, which holds approximately 400 gallons will be used to house media for beneficial bacteria. This media will consist of medium (2-3mm) sand which will have the return water from the filter pumped up through the bottom of the sand. This will greatly increase the surface area for beneficial bacteria (BB). The upper basin will need to be drained so the water lines that feed it can be reworked so that water will enter the basin from its bottom instead of approximately mid-way up. The lower basin will also get some plumbing rework done to it to as the drain needs to be modified as well as a secondary water return from the pump. The whole thing was obviously designed as a water feature without much thought for fish. The bottom of the lower basin is flat. In a perfect world it would be sloped towards the drain. This would greatly effect the way water circulates and how waste makes its way to the pickup (drain) for the pump. I have suggested that the pond be drained and the koi moved, so that the bottom of the lower basin can have a sloped concrete layer installed, but they are not enthusiastic about this at all and it will likely not happen. The filter will consist of three, possibly 4, 55 gallon plastic drums. Drums #1 & 2 will both have vortex filters. These are simple and inexpensive to construct and do a fantastic job of removing solid waste and clarifying the water. They are also extremely simple to maintain as there will be a bottom drain with a valve attached. With weekly partial draining of drums #1 and 2 the majority of the solid waste will be disposed of. Since they adjoin the river it would be a simple matter for this to drain into the river, but I am trying to get them to use the waste to fertilize and water their extensive selection of plants. DIY Vortex (aka swirl) Filter https://www.youtube.com/watch?v=-mLPro9N7FQ (youtube.com/watch?v=-mLPro9N7FQ) More detailed info about it is here: http://www.earthangroup.com.au/building-simple-swirl-filter/ After drums 1 and 2 the water will go to drum #3 for polishing and biological filtration. DIY Sand Filter (youtube.com/watch?v=QQUtBrEcaB4) After this step the water should be polished to a fine degree, but we will see. If I am not completely happy with the result I will add drum #4 for final polishing before the water goes back to the pond. Water changes should be minimized because the lower basin will be partially stocked with aquatic plants such as water hyacinths. I want to corral these so they are partially under the overhang of the upper basin. Hyacinths work extremely well at reducing and eliminating nitrates from fish waste. With nitrates removed/reduced algae and green water is eliminated for the most part. Since the price of city water is ridiculous here in Dumaguete (90 centavos/gallon!) it is cost prohibitive to do large water changes so we will also be constructing a very large water catch system. The church has a number of buildings and has a massive roof area. Some of the roof area is fully guttered (about 1/2) while other sections are not. Even with just 1/2 the roof guttered I think we will be able to catch enough water during the rainy season to keep this, and 3 other ponds full. Right now all of the rain water goes on the ground, which all parties agree is a waste. Here in Dumaguete rainwater is acidic because of air pollution. To "sweeten" the water and raise the pH we will be using crushed coral placed in mesh bags. I have a pH as well as other water test kits so it will be a simple matter to see if the coral is enough to do the job or if another step will be needed such as adding baking soda which is a completely fish safe alternative to raise water pH. When all is said and done I hope to have pictures that show the results. I will have to rely on the church though as my Nikon has lense issues and needs to be repaired. Most of the stuff that will be needed to do all of this will be donated, but I hope to compile an accurate list of what was used and the quantities involved so I can come up with an approximate cost if others want to do something similar. They are in the process of acquiring my "want list" now. I told them it would be nice if we could get it all done before the rainy season really kicks in here which historically starts in June, but time will tell if that happens. Stay tuned.......