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Diagrams of a Gravity-Fed Pond/Filter System.

The above is a diagrammatic representation of a rectangular pond measuring 18ft long x 10ft wide x 5ft deep. The surface area is 180sqft. and volume is 25.5cu.m or 5,654gal(UK). The main filter covered by decking measures 18ft long x 3ft wide x 4ft deep. The surface area is 54sqft and volume is 6.1cu.m or 1,357gal(UK). The surface area of the filter is 30% that of the pond. This does not include the veg. filter that overhangs the pond.

The above shows the Features of the pond/filter system. There is a waterfall, 2 venturis(V), 2 bottom-pushes(BP), a surface skimmer(Sk) and 2 bottom drains(BD) in the pond. The main filter consists of 5 chambers, Ch1 to Ch5. All chambers except Ch4 have 3in. floor drains(d). There is an additional chamber, the Dry Sump attached to the filter.

The above shows the electrical wiring and piping of the pond/filter system. There should be one electrical socket for each electrical appliance. The last chamber(Ch5) has 2 pumps and a UV unit. P1 supplies BP1, BP2 and the waterfall via the veg. filter. P2 supplies V1 and V2. The UV unit (50-60W) is optional. The surface skimmer (Sk) opens into Ch1. The air-pump aerates the biomedia in Ch4 via a few air-tubings. BD1 and BD2 (6in bottom drain pipes) open upward into Ch1 via a "T" and drain into the dry sump. The 2in. floor drains(d) in the veg filter also drain into the dry sump. So do the 3in. floor drains in the main filter. All outlets into the dry sump are controlled by valves except the outlet from the 3in. floor drains in the main filter which are plugged by pull-pipes. The pump(P3) in the dry sump is activated by rising water level. It pumps waste water to the sewage or an external drainage system.

The above illustrates the mechanism and flow dynamics during the 3 modes of operation, that is, 1)Normal Operation. Here, the pull-pipes or stand-pipes for the 3in. floor drains are always in place to prevent water loss from filter. These pipes can double as overflow pipes when there is rain. 2)Flushing of Bottom Drains. This can be done daily or less frequently. It merely involves turning open the valves in BD1 and BD2 in the dry sump for a few seconds, and then closing it. Waste from the bottom of the pond and some from Ch1 will be flushed away. 3)Cleaning of Chambers and Media. This can be done once a month or less frequently. All decking is removed. P1, P2 and the air-pump are shut off. The pull-pipe for the 2 bottom drains, BD1 and BD2 are put in place to prevent water loss from the pond during cleaning. Then the pull-pipe for the 3in. floor drains in Ch1 and Ch2 are removed. Water levels in Ch1 and Ch2 drop. The debris on the floor is agitated so that it will flow out with the water. The brushes are removed for cleaning. The walls and floor of Ch1 and Ch2 are scrubbed. Some pond water is then released into Ch1 thru BD1 and BD2 by unplugging and replugging to flush the bottom drains. After draining all the water from Ch1, the clean brushes are replaced and the pull-pipes for the floor drains are plugged in place. The pull-pipes for BD1 and BD2 are unplugged to release some pond water into Ch1 and Ch2 again. This water will come in handy when Ch4 is cleaned. Next, the pull-pipe for the floor drain in Ch3 is unplugged. This causes water from Ch3 and Ch4 to drain out. Buckets of water from Ch1 are used to flush the Japanese mats. The debris from the mats will drain out thru the floor drain in Ch3. Once the mats are reasonably flushed, the pull-pipe is plugged into the floor drain in Ch3. Finally the pull-pipe in Ch5 is unplugged. Water in Ch5 drains out. The walls and floor in Ch5 are scrubbed and cleaned. The pull-pipe is plugged in. This is the sequence in which the filter chambers should be cleaned. Pond water is released into the rest of the filter via Ch1 by unplugging the pull-pipes for BD1 and BD2. The water level is topped up with fresh water from the tap which must be dechlorinated. When a sufficient water level is achieved for smooth water flow throughout the filter, the pumps P1 and P2 are switched on. The whole system goes into Normal Operation mode again.

The above illustrates 1)the cross sectional view of the filter with it's different types of partitions and the mechanical (brushes) and biological (mats) media. Air stones (not shown) should be placed in Ch4. The pull-pipes and their drainage system are easily appreciated in this view. 2)the top view of the filter. The Japanese mats should be arranged in the manner shown for effective aeration and water flow.

The above shows the cross sectional view of a surface skimmer which is gravity fed. These should be located near the wall opposite water returns like waterfalls or venturis. The joint between the vertical and the horizontal limbs should not be sealed. This is to allow for adjustments (tilting) of the vertical limb to ensure optimal water intake from the surface of the pond.