For the past 4 years, we have been working with a biological sand water filter applied to filtering water that is used in a pond. The preceding link takes you to one of our other websites where the assembly of the filter is shown in detail, along with some photos of the pond. The filter has continued to work flawlessly since August of 2010. As of today (December 23, 2014) the filter is still working and keeping the water crystal clear. Birds, and squirrels use the pond continuously. The water stays absolutely clear 24/7, with the exception of the times when it is frozen. Every year so far, the pond has frozen along with the filter. There has been no damage with the exception of the water level falling considerably when the pond freezes over. There are no fish in the pond, but there is an abundance of organic material constantly falling into the pond. We clean out the bottom once a year. That is all we have to do with the exception of adding some harvested roof water during the summer months.
All that is used in the filter is sand and gravel. The sand does not need to be changed. The only filter maintenance needed involves taking the top off of the barrel and gently agitating the surface of the sand inside to break loose the heavy layer of active organisms in the biolayer. That’s it. Very simple. Organisms in the water grow on the surface of the sand and literally eat the organic material in the water leaving only purified water to flow down through the rest of the sand and back into the pond. The filter has an overflow that directs back into the pond so no output flow regulator is necessary. Gravity does all that work on its own.