Take filter out of service and drain down, leaving some water on top of anthracite. Allow the filter to soak or preferably, air scour for at least two hours. A longer cleaning cycle will generally produce cleaner media. Initiate a normal water backwash. It may be necessary to extend the duration of backwash before putting the filter back into service.
Sodium hydroxide is available in dry or liquid form.
Using dry product may alleviate certain safety-related concerns associated with application in a aqueous form. The solid form is shipped in 50 lb. Solid sodium hydroxide pellets may take several minutes to dissolve, while liquid disperses throughout the filter more readily. The effectiveness of the cleaning process is dramatically improved by air scour, which may help reduce soaking time and will loosen debris. A temporary air scour system may be set up by introducing air through a fabricated PVC pipe grid that rests on top of the backwash troughs and extends down into the media.