Aluminium brasses are often used in heat exchangers of industrial plants due to its excellent corrosion protection behaviour. Besides their good resistance to biofouling (associated to the release of toxic copper ions), when immersed in seawater, colonies of bacteria quickly build up a biofilm that cover the metallic surface. Microorganisms influence corrosion by changing the electrochemical conditions at the alloy/solution interface, creating an environment that is completely different from that of the bulk medium in terms of pH, dissolved oxygen, organic and inorganic species concentrations. The objective of this work was to study the influence of hydrodynamics and pH on the electrochemical behaviour of Al brass (76% Cu, 22% Zn and 2% Al) and the surface chemical composition of oxide layers. For that purpose, electrochemical measurements (corrosion potential (Ecorr) vs time, polarization curves, electrochemical impedance spectroscopy (EIS)) in static conditions and using a rotating ring electrode (RRE) were performed in aerated filtered natural seawater (FNSW) at different pH (8.0, 6.0 and 3.7), and combined to surface analyses by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). After 1 h of immersion, the measurements indicate no influence of the bulk pH on the electrochemical behaviour of the Al brass, while the increase of the RRE rotation speed induces more cathodic Ecorr values and a significant decrease of the anodic charge transfer resistance. Polarization curves show similar shape in static conditions and with the RRE but an increase of the current density is visible with the RRE. A model is proposed to analyse the impedance data.