The type and properties of the filtration solution affect the formation and thickness of the cake layer on the membrane surface. This study aims to identify the effect of the acidity of Sodium Alginate (SA) solution on the filtration profile and cake layer formation on the Polyethersulfone/Aerosol OT (PES/A-OT) membrane surface. The filtration process was carried out using a single hollow fiber module by the pressure-driven outside system with the feed flowing from the membrane's outer wall and clean water collected on the inside of the hollow fiber membrane. The pH solution was tested at neutral, acid, and bases, and the filtration performance of the membrane was evaluated based on water flux recovery ratio (FRR) and cake formation on the membrane surface. The results showed that SA solution with neutral pH produced the best FRR (up to 87.3) and the thinnest cake layer formation. © 2021, Rasayan Journal of Chemistry, c/o Dr. Pratima Sharma. All rights reserved.