An apparatus for dispensing a vapor phase reactant to a reaction chamber is disclosed. The apparatus may include: a vessel having an inner volume configured to contain a liquid chemical; an array of sensors configured for detecting a fill level of the liquid chemical disposed within the inner volume, wherein the array of sensors are vertically distributed within the inner volume with an irregular vertical interval between adjacent sensors. The apparatus may also include: an inlet disposed in the vessel and configured for providing a carrier gas into the inner volume; and an outlet disposed in the vessel and configured for dispensing the vapor phase reactant from the inner volume to the reaction chamber. A sensor array for detecting the fill level of a liquid chemical is also disclosed, as well as methods for dispensing a vapor phase reactant to a reaction chamber.