A multi-tank system for preparing fluids for hydraulic fracturing of reservoirs and methods of injecting the prepared fluid upstream from pumping units are disclosed. The multi-tank system allows for a proppant slurry to be continuously formed and mixed with a proppant carrier in staggered phases to form a fracturing fluid. This fracturing fluid can then be injected into the reservoir at normal injection pressures, thus reducing wear and downtime on the blender, and allowing continuous flow of proppant.