Harmsco Betterfilter BF105SC 28" 105 SqFt Single Cluster Filter Cartridge 105 gpm / 39.37 gpm. Betterfilters® The original filter for swimming pools features the patented upflow design that makes Harmsco Betterfilters the safest swimming pool filter line in the world. Air cannot be trapped inside a Harmsco Betterfilter during operation. No need for tricky manual air relief during startup. No need to make provisions for wasteful backwash disposal. No moving parts, no complicted valves... just simple, efficient, safe, quality filtration.