Matala offers a 9″ membrane air diffuser assembly that features a hollow base that can be filled with sand or gravel. This eliminates the need for bricks and straps to get the diffuser to sink. Available in both a single head or dual head assemblies. â single head handles airflow 1. 4 – 4. 2 cfm. recommended for a 25 lpm – 80 lpm air pump.