Following the failure of filter 4, in early June, 2013 the following modifications were made on June 5, 2013 when the filter was restarted:
The top 3 inches of sand was removed and changed from .25mm effective size to .35 mm effective size. The inside of the barrel was scored horizontally using #60 grit sandpaper. This was done around the entire inside surface in a 3.5 inch wide band at the top layer where the .35 mm sand sits on top of the .45mm sand.
The sand used on the top is #30 Unimin industrial quartz processed using a 30 mesh stainless steel screen. The sifted sand used consists of the 60 percent retained by weight on top of the 30 mesh screen. The 30 mesh screen is square weave stainless steel; .012″ wire size, and .0213″ opening (.54mm). Supplier is McNichols. The part number of the wire screen is: 3830123610.
The flow rate at initial set up was .203 cubic meters per hour. This works out to an output of 55 litres per hour.
30 gallons of clean filtered water was run through the filter to clean it out.