Hot Tub Compatible With Cal Spas Filter 50 SQ Open Ends FIL50-5D13H2OE-3. Filter Cartridge 50 SQ FT x 5"ODx 13"Hx 2"IDx OPEN ENDS. Our replacement cartridge filter gives you the right balance of simple operation, maintenance, affordability, and quality that could reduce your regular maintenance budget significantly. The filtering area is not limited and there are no potential contaminants seeping out during the filtration process therefore maximizing the effectiveness of filtering out any accumulating bacteria, mold, and algae that can be present in hot tubs and spas. This antimicrobial property gives your hot tub and spa constant protection against microbes and microorganisms invisible to the naked eye.