Methods for polymerization of an olefin monomer and polymers formed therefrom are described herein. The methods generally include introducing an olefin monomer and a diluent carrier liquid into a polymerization reactor, supplying at least one polymerization catalyst system to said polymerization reactor, circulating said diluent liquid in said olefin monomer within said reactor while polymerizing said olefin monomer in the presence of said catalyst system to produce a slurry of polymer fluff particle in said diluent carrier liquid, recovering polymer particles from said polymerization reactor, initiating a localized pressure drop in said reactor to produce a pressure wave in which the pressure varies with time, measuring said pressure wave and characterizing said pressure wave as either a hydraulic pressure curve or a non-hydraulic pressure curve, which is characteristic of a gas being present in said slurry and in response to the characteristic of said pressure curve as being a non-hydraulic pressure curve, reducing the olefin monomer concentration in said reactor.