Never did a backwash myself. Taking over from my pool service in a week or two. Have a 48' DE filter, says it takes 4.8# or 10 coffee cans. I don't drink coffee.... Pool School says add 80%, so about 4#, after each backwash. Does 4# translate to "cups"? The previous owner left a 2 cup measure in the DE bag. I may just bring home a 10# scale from work and weigh 4# worth... I could see DE having different densities depending on humidity.