Mammalian synapses facilitate high-frequency sustained neurotransmission through the fusion of synaptic vesicles (SVs) with the presynaptic membrane, followed by rapid recycling of SV machinery, including SNARE components, SV proteins, and membrane lipids over milliseconds to minutes. Visualizing these SV exo-endocytosis events is challenging due to their speed and nanoscale localization. To address this, we identified candidate SV proteins with abundant representation on SVs for precise labelling, aiming to enhance contrast. Conventional methods like over-expression, antibody-based labelling, and small molecule tags can compromise protein function and targeting, leading to misinterpretation of SV cycling mechanisms. Therefore, we employed the CRISPR-Cas9 system (TKIT method) for endogenous labelling of candidate proteins. We developed a library of potential target sequences, tested their efficiency in cell lines, and selected optimal guide RNAs (gRNAs). Utilizing two gRNAs and a Donor for Knock-In, we achieved high labelling precision of SV fusion events. Our objective is to detect changes in intraluminal SV pH upon fusion and recycling to investigate fusion and compensatory endocytosis mechanisms. To achieve this, we knocked-in super ecliptic pHluorin (SEP) into the luminal domain of candidate SV proteins. Following successful incorporation of the fluorescent tag, we assessed primary neuron fluorescence with field stimulation. Following this we detected and evaluated SV fusion and recycling. This approach demonstrates an effective methodology for labelling, visualizing, and studying SV protein recycling at the presynapse.