A pumping system and method for blending hydraulic fracturing fluids includes a liquid additive holding tank having an outlet at a bottom of the holding tank, a first sensor at a first location in the holding tank adjacent a lower portion of the holding tank, and a second sensor at a second location in the holding tank above the first location. The pumping system further includes a liquid additive pump to deliver fluid gravity fed from the outlet of the holding tank, a chemical transfer pump to pump fluid into the holding tank in response to receiving a first signal that a fluid level of the holding tank is below the first sensor and cease to pump fluid into the holding tank in response to receiving a second signal from the second sensor indicating the fluid level is above the second sensor.