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A slow sand filter can be used to filter the water used in a pond or fountain.
The result is very clean water.
See a video of the filter in operation here
2010-07-10: The pond filter has been started.
2010-11-27: The pond filter has been frozen (inoperable) for 5 days and is still frozen; however the pond is mostly thawed out. The filter froze from the outside inward. This has caused the output pipe to stay frozen as it is on the inside of the container within 1/4 inch of the wall - where the filter is still frozen on the inside - rather than outside of the container where the temperature has warmed up to above freezing. The filters with the output pipes on the outside are partially functional now, as those output pipes warm up faster.
2011-01-03: The pond filter has been frozen for 6 days now, as well as the top 2 inches of the pond. Before the freezing weather, water samples went in for testing. We will be looking at the turbidity and numbers of Coliform bacteria in the filter output water. Expect test results about 2 weeks from 2011-01-01.
2011-09-29: The pond filter is still functional. There has been one modification: an overflow pipe that feeds back into the pond has been added to the top of the filter. This allows the water that backs up (as a result of flow reduction due to biofilm density increase) to flow back into the pond rather than spilling out the top of the filter. This prevents water loss by giving extra time to wet harrow the sand surface - when water flows from the overflow pipe its time to wet harrow the sand surface. The little pond pump has seen much abuse - freezing water, running dry (the raccoons actually dragged it out which left it running ouside of the pond over night), and plugging up with muck from the bottom of the pond - and it still is working fine.
The result is very clean water.
See a video of the filter in operation here
2010-07-10: The pond filter has been started.
2010-11-27: The pond filter has been frozen (inoperable) for 5 days and is still frozen; however the pond is mostly thawed out. The filter froze from the outside inward. This has caused the output pipe to stay frozen as it is on the inside of the container within 1/4 inch of the wall - where the filter is still frozen on the inside - rather than outside of the container where the temperature has warmed up to above freezing. The filters with the output pipes on the outside are partially functional now, as those output pipes warm up faster.
2011-01-03: The pond filter has been frozen for 6 days now, as well as the top 2 inches of the pond. Before the freezing weather, water samples went in for testing. We will be looking at the turbidity and numbers of Coliform bacteria in the filter output water. Expect test results about 2 weeks from 2011-01-01.
2011-09-29: The pond filter is still functional. There has been one modification: an overflow pipe that feeds back into the pond has been added to the top of the filter. This allows the water that backs up (as a result of flow reduction due to biofilm density increase) to flow back into the pond rather than spilling out the top of the filter. This prevents water loss by giving extra time to wet harrow the sand surface - when water flows from the overflow pipe its time to wet harrow the sand surface. The little pond pump has seen much abuse - freezing water, running dry (the raccoons actually dragged it out which left it running ouside of the pond over night), and plugging up with muck from the bottom of the pond - and it still is working fine.
 Drill holes in the drain pipes with a no.10 bit |
 Assemble the drain pipe system |
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 The 90 on the output is threaded on the top end |
 A flexible connection using garden hose and pipe clamps is necessary using a 1/2 inch threaded adapter on each end with pipe clamps to secure them. A 1/2 inch threaded adapter will screw into 5/8 inch od hose on a warm day |
 Use a 3/4 inch spade bit to drill the hole |
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 The threaded adapter will "thread" the the hole made by the 3/4 inch bit Then the adapter is loosened and screwed into the 90 at the same time it is re-threaded back into the threads it made in the barrell |
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 Wash the pea gravel until the water runs clear |
 The pea gravel should cover the drain pipes by about 1 inch |
 Washed nsf 61 approved filter sand is used. Available at hardware stores "Target" filter sand website |
 Fill the barrel with water BEFORE you add sand - prevents air bubbles See Note below |
 Finished filter in operation.(The reflection on top is rain water) |
 Filtered pond This test pond has raccoons,birds, and squirrels, using it. This is six weeks of use. Without the filter this water would be stagnant and filled with bad bacteria. It holds 118 litres of water. |
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 This is the Filtered pond test pond at its 14th week since filling. Still clear. Still 118 liters |
 Unfiltered pond As of 2010-10-01 This test pond has been filled by rain water since 2010-08-01 It contains 212 litres of water and there is no filter circulating the water. (this is a different pond container than the above pictures and it is 100 feet to the north of the filtered pond in a similar setting |
 Unfiltered pond This is the unfiltered water at week 12: Oct 31 2010 slightly over 275 litres now because of rainfall This pond will need to be emptied, as it is a hazard because of mosquitoes. |
 Filtered pond This is the test pond with the filtered water at week 17: Oct 31 2010. Still clear, still 118 liters. No mosquitoes. The leaves at the bottom are visible because the water is clear |
 This is the Filtered pond water week 17, Oct 31 2010 As of 2010-11-07, three 4 inch goldfish were put into the above pictured pond. |
 This is the Unfiltered pond water week 12, Oct 31 2010 |
 Closeup of the Filtered pond as of 2010-10-31 Note the waterline on the brick. |
 This is the Filtered pond water laser reflection 2010-11-04 This is water directly from the pond |
 This is the Unfiltered pond water laser reflection closeup 2010-11-04 |
In the images to the left The lasers show relative turbidity; a brighter line indicates more solids in the water sample. The unfiltered water is heavily contaminated with solids. The same laser, the same camera the same settings, and the same lighting were used on all images. All of the containers are the same type of commercial food jars The images were resized - no other processing was done.Compare these to the four different commercial bottled water samples below. |
 bottled water |
 bottled water |
 bottled water |
 bottled water |
Note Air bubbles in a slow sand filter will cause the "good" bacteria to die and decompose - thus fouling the entire filter and causing horrible odors and nasty anaerobic bacteria to grow resulting in the need to completely clean the sand and gravel and sterilize it also. It's a reall mess if it happens - trust me - you don't want air bubbles in a slow sand filter. Filling it with water first does two things: it lets you check for leaks before you have put (in this case) 400 plus pounds of sand in and keeps air pockets from forming in the sand as it is added. I've been through this already with a much larger filter and had to shovel out 1000 lbs of sand and sterilize it amdist the foul odor. Very unpleasant indeed. An ounce of prevention would have been worth a ton of cure! (I had to shovel the 1000 lbs of sand 2 extra times: once out (to clean it), and then back in again)
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