Hayward Perflex® EC50AC 25 SqFt Modular DE Filter. Perflex Extended-Cycle diatomaceous earth (DE) filters provide crystal clear, sparkling water at an economical price. Proven over many years, Perflex has set the standard in swimming pool filtration by incorporating the Flex-Tube™ design in combination with diatomaceous earth, the most effective filter media available. The result is superior water clarity, extended filter cleaning cycles - and no backwashing required.