The properties of nucleating and growing struvite crystals are important aspects to pellet agglomeration and growth mechanisms in fluidized bed reactors (FBR). A new approach, using a laser to sense crystals of approximately 650 nm, was used to measure the induction time of nucleating struvite. The ability of the laser to indicate an approximate size ensured the presence of crystals in solution for zeta potential (zeta) measurements. This is the first study where zeta was measured for nucleating and growing struvite crystals, and it was not negative like aged crystals; it changed over time as the solution conditions changed, generally started positive and became more negative as precipitation proceeded. The time where zeta approximate to 0 can be related to supersaturation ratio (SSR) and optimal agglomeration locations within FBR systems. SSR values between 2 and 6 are recommended to reduce zeta values for extended periods and to improve struvite FBR agglomeration processes. (C) 2019 Elsevier B.V. All rights reserved.